diff --git a/.env.example b/.env.example
index f51f6f1..b530464 100644
--- a/.env.example
+++ b/.env.example
@@ -16,3 +16,7 @@ TLS_KEY_FILE=/etc/travel-planner/tls/tls.key
 OIDC_ISSUER=https://idp.example.invalid/realms/travel-planner
 OIDC_AUDIENCE=travel-planner-api
 OIDC_CLIENT_ID=travel-planner-web
+# OIDC_CLIENT_SECRET: this client is confidential (holds a secret). Never commit
+# a real value here; supply it only via the deployment host's secret store /
+# the developer's own shell environment.
+OIDC_CLIENT_SECRET=change-me-outside-source-control
diff --git a/README.md b/README.md
index f2cf9cc..4d105d6 100644
--- a/README.md
+++ b/README.md
@@ -19,25 +19,32 @@ docs/       Specs, plans, and architecture documentation
 ```bash
 pnpm install
 pnpm dev:infra
-DATABASE_URL=postgresql://travel_planner:travel_planner_dev@localhost:5432/travel_planner \
-REDIS_URL=redis://localhost:6379 \
-OIDC_ISSUER=https://idp.example.invalid/realms/travel-planner \
-OIDC_AUDIENCE=travel-planner-api \
-  pnpm --filter backend start:api
-pnpm --filter frontend start
 ```
 
-Run pending migrations against the dev database before starting the API for the first time:
+`pnpm dev:infra` starts local PostgreSQL/Redis (see `compose.dev.yml`); `pnpm dev:infra:down` stops them.
+
+Set the required OIDC env vars once per shell before running the backend. **`OIDC_CLIENT_SECRET` is a real secret — set it directly in your own shell, never commit it, never paste it into a shared/logged terminal.** `OIDC_AUDIENCE` should be set to the same value as `OIDC_CLIENT_ID` unless your IdP issues a distinct API audience.
 
 ```bash
 export DATABASE_URL=postgresql://travel_planner:travel_planner_dev@localhost:5432/travel_planner
 export REDIS_URL=redis://localhost:6379
-export OIDC_ISSUER=https://idp.example.invalid/realms/travel-planner
-export OIDC_AUDIENCE=travel-planner-api
-pnpm --filter backend build:api && node backend/dist/apps/api/src/migration.js
+export OIDC_ISSUER=https://auth.forgecore.work
+export OIDC_CLIENT_ID=client_a297fd8d9c1f47a79d3600ea0c96984
+export OIDC_AUDIENCE=$OIDC_CLIENT_ID
+export OIDC_CLIENT_SECRET=<your-client-secret>   # never commit this value
 ```
 
-`pnpm dev:infra` starts local PostgreSQL/Redis (see `compose.dev.yml`); `pnpm dev:infra:down` stops them.
+Run pending migrations against the dev database (first time only), then start the API and frontend:
+
+```bash
+pnpm --filter backend build:api && node backend/dist/apps/api/src/migration.js
+pnpm --filter backend start:api
+pnpm --filter frontend start
+```
+
+Open `http://localhost:4200`. The Angular dev server proxies `/api/*` and `/health/*` to the API on `localhost:3000` (see `frontend/proxy.conf.json`), so no CORS configuration is needed locally. Make sure the IdP client `client_a297fd8d9c1f47a79d3600ea0c96984` allows the redirect URI `http://localhost:4200/auth/callback`.
+
+This IdP client is **confidential** (it has a client secret), so the Authorization Code + PKCE token exchange happens server-side via `POST /api/v1/auth/session` (see "OIDC client type" below) — the secret never reaches the browser.
 
 ## Quality gates
 
@@ -76,8 +83,9 @@ Production Docker Compose (`compose.yml`) publishes **exactly one** host port, o
 
 ## Phase 02 status: OIDC auth, users, and trip core complete
 
-- Authentication: OIDC Authorization Code + PKCE against an external IdP (`oidc-client-ts` on the frontend, `jose`-based bearer-token verification on the backend). No local password storage; users are keyed by the OIDC `sub` claim and just-in-time provisioned on first login.
-- New required backend env vars: `OIDC_ISSUER`, `OIDC_AUDIENCE` (validated fail-fast like `DATABASE_URL`/`REDIS_URL`). New frontend build-time values: `OIDC_ISSUER`, `OIDC_CLIENT_ID` (baked into the production bundle by `docker/edge.Dockerfile`, never read from the container at runtime).
+- Authentication: OIDC Authorization Code + PKCE against an external IdP. No local password storage; users are keyed by the OIDC `sub` claim and just-in-time provisioned on first login.
+- **OIDC client type:** this deployment's IdP client is confidential (has a client secret), not a plain public/PKCE-only SPA client. A client secret must never be embedded in a browser bundle, so the frontend performs only the browser-side Authorization Code + PKCE redirect (hand-rolled PKCE in `frontend/src/app/auth/pkce.ts`, no `oidc-client-ts` dependency); the resulting `code` + PKCE `code_verifier` are then POSTed to the backend's `POST /api/v1/auth/session` (unauthenticated by design — there is no token yet), which performs the actual code-for-tokens exchange using `OIDC_CLIENT_SECRET` server-side (`TokenExchangeService`) and returns only `{ accessToken, expiresIn }` to the frontend — `refresh_token`/`id_token` are never forwarded. If a future deployment instead uses a public PKCE-only client, this proxy step could be skipped in favor of a direct frontend-to-IdP exchange, but the current IdP requires it.
+- New required backend env vars: `OIDC_ISSUER`, `OIDC_AUDIENCE`, `OIDC_CLIENT_ID`, `OIDC_CLIENT_SECRET` (validated fail-fast like `DATABASE_URL`/`REDIS_URL`; `OIDC_CLIENT_SECRET` is a real secret, never committed). New frontend build-time values: `OIDC_ISSUER`, `OIDC_CLIENT_ID` (non-secret; baked into the production bundle by `docker/edge.Dockerfile`, never read from the container at runtime).
 - Real, versioned database migrations (`node-pg-migrate`, files under `backend/migrations/`) replace the Phase 01 no-op `migration.ts` body; the container command contract (`node backend/dist/apps/api/src/migration.js`) is unchanged. Database access goes through `kysely` (a type-safe query builder, not an ORM) over the existing `pg.Pool`; there is no schema auto-sync anywhere.
 - New routes: `GET/PUT /api/v1/users/me`(`/preferences`), `GET/POST /api/v1/trips`, `GET/PATCH/DELETE /api/v1/trips/:tripId`, `GET/PUT /api/v1/trips/:tripId/settings`, `GET/PATCH/DELETE /api/v1/trips/:tripId/members(/:memberId)`, `POST/GET/DELETE /api/v1/trips/:tripId/invitations(/:invitationId)`, `POST /api/v1/invitations/:token/accept`, `GET/POST/PATCH/DELETE /api/v1/trips/:tripId/travelers(/:travelerId)`, `GET/PUT/DELETE /api/v1/trips/:tripId/preference-overrides(/:overrideId)`.
 - Authorization is enforced backend-side by `OidcAuthGuard` (who) and `TripMembershipGuard` (trip access + `@TripRoles('OWNER')`), never only in the frontend. `TripMember` and `Traveler` are independent tables — a `Traveler` never implies or requires trip membership.
diff --git a/backend/apps/api/src/api.module.ts b/backend/apps/api/src/api.module.ts
index 4699d94..841334e 100644
--- a/backend/apps/api/src/api.module.ts
+++ b/backend/apps/api/src/api.module.ts
@@ -6,12 +6,14 @@ import { HealthModule } from './health/health.module';
 import { VersionModule } from './version/version.module';
 import { UsersApiModule } from './users/users.module';
 import { TripsApiModule } from './trips/trips.module';
+import { AuthApiModule } from './auth/auth.module';
 
 @Module({
   imports: [
     ConfigurationModule,
     HealthModule,
     VersionModule,
+    AuthApiModule,
     UsersApiModule,
     TripsApiModule,
   ],
diff --git a/backend/apps/api/src/auth/auth-session.controller.spec.ts b/backend/apps/api/src/auth/auth-session.controller.spec.ts
new file mode 100644
index 0000000..44964b1
--- /dev/null
+++ b/backend/apps/api/src/auth/auth-session.controller.spec.ts
@@ -0,0 +1,23 @@
+import { AuthSessionController } from './auth-session.controller';
+
+describe('AuthSessionController', () => {
+  it('POST /auth/session exchanges the authorization code via the token exchange service', async () => {
+    const tokenExchange = {
+      exchangeAuthorizationCode: jest
+        .fn()
+        .mockResolvedValue({ accessToken: 'at-1', expiresIn: 3600 }),
+    };
+    const controller = new AuthSessionController(tokenExchange as never);
+
+    const dto = {
+      code: 'code-1',
+      codeVerifier: 'verifier-1',
+      redirectUri: 'http://localhost:4200/auth/callback',
+    };
+    await expect(controller.createSession(dto)).resolves.toEqual({
+      accessToken: 'at-1',
+      expiresIn: 3600,
+    });
+    expect(tokenExchange.exchangeAuthorizationCode).toHaveBeenCalledWith(dto);
+  });
+});
diff --git a/backend/apps/api/src/auth/auth-session.controller.ts b/backend/apps/api/src/auth/auth-session.controller.ts
new file mode 100644
index 0000000..d78eb71
--- /dev/null
+++ b/backend/apps/api/src/auth/auth-session.controller.ts
@@ -0,0 +1,15 @@
+import { Body, Controller, Post } from '@nestjs/common';
+import { TokenExchangeService } from '../../../../libs/auth/src';
+import type { AuthorizationCodeExchangeRequest, AuthorizationCodeExchangeResult } from '../../../../libs/auth/src';
+
+@Controller('auth')
+export class AuthSessionController {
+  constructor(private readonly tokenExchange: TokenExchangeService) {}
+
+  @Post('session')
+  createSession(
+    @Body() dto: AuthorizationCodeExchangeRequest,
+  ): Promise<AuthorizationCodeExchangeResult> {
+    return this.tokenExchange.exchangeAuthorizationCode(dto);
+  }
+}
diff --git a/backend/apps/api/src/auth/auth.module.ts b/backend/apps/api/src/auth/auth.module.ts
new file mode 100644
index 0000000..c1d5fe8
--- /dev/null
+++ b/backend/apps/api/src/auth/auth.module.ts
@@ -0,0 +1,7 @@
+import { Module } from '@nestjs/common';
+import { AuthSessionController } from './auth-session.controller';
+
+@Module({
+  controllers: [AuthSessionController],
+})
+export class AuthApiModule {}
diff --git a/backend/libs/auth/src/auth.module.ts b/backend/libs/auth/src/auth.module.ts
index 23f9a47..72b7386 100644
--- a/backend/libs/auth/src/auth.module.ts
+++ b/backend/libs/auth/src/auth.module.ts
@@ -2,11 +2,17 @@ import { Global, Module } from '@nestjs/common';
 import { UsersLibModule } from '../../users/src';
 import { OidcDiscoveryService } from './oidc-discovery.service';
 import { OidcAuthGuard } from './oidc-auth.guard';
+import { TokenExchangeService } from './token-exchange.service';
 
 @Global()
 @Module({
   imports: [UsersLibModule],
-  providers: [OidcDiscoveryService, OidcAuthGuard],
-  exports: [OidcDiscoveryService, OidcAuthGuard, UsersLibModule],
+  providers: [OidcDiscoveryService, OidcAuthGuard, TokenExchangeService],
+  exports: [
+    OidcDiscoveryService,
+    OidcAuthGuard,
+    TokenExchangeService,
+    UsersLibModule,
+  ],
 })
 export class AuthModule {}
diff --git a/backend/libs/auth/src/index.ts b/backend/libs/auth/src/index.ts
index 03eba96..7165225 100644
--- a/backend/libs/auth/src/index.ts
+++ b/backend/libs/auth/src/index.ts
@@ -1,3 +1,4 @@
 export * from './oidc-discovery.service';
 export * from './oidc-auth.guard';
+export * from './token-exchange.service';
 export * from './auth.module';
diff --git a/backend/libs/auth/src/oidc-discovery.service.spec.ts b/backend/libs/auth/src/oidc-discovery.service.spec.ts
new file mode 100644
index 0000000..64ef8d0
--- /dev/null
+++ b/backend/libs/auth/src/oidc-discovery.service.spec.ts
@@ -0,0 +1,47 @@
+import { OidcDiscoveryService } from './oidc-discovery.service';
+import type { AppEnvironment } from '../../configuration/src';
+
+describe('OidcDiscoveryService', () => {
+  const environment: AppEnvironment = {
+    databaseUrl: 'postgresql://u:p@postgres:5432/db',
+    redisUrl: 'redis://redis:6379',
+    oidcIssuer: 'https://idp.example.test',
+    oidcAudience: 'client-1',
+    oidcClientId: 'client-1',
+    oidcClientSecret: 'secret-1',
+    appVersion: 'dev',
+    teamCityBuildNumber: 'local',
+    sourceRevision: 'local',
+  };
+
+  it('fetches the discovery document once and exposes the token endpoint', async () => {
+    const fetchMock = jest.fn().mockResolvedValue({
+      ok: true,
+      json: () =>
+        Promise.resolve({
+          jwks_uri: 'https://idp.example.test/oidc/jwks',
+          token_endpoint: 'https://idp.example.test/oidc/token',
+        }),
+    });
+    (globalThis as { fetch: typeof fetch }).fetch = fetchMock as never;
+
+    const service = new OidcDiscoveryService(environment);
+    await service.onModuleInit();
+
+    expect(fetchMock).toHaveBeenCalledWith(
+      'https://idp.example.test/.well-known/openid-configuration',
+    );
+    expect(service.getTokenEndpoint()).toBe(
+      'https://idp.example.test/oidc/token',
+    );
+    expect(service.getIssuer()).toBe('https://idp.example.test');
+    expect(service.getAudience()).toBe('client-1');
+  });
+
+  it('throws when asked for the token endpoint before discovery has completed', () => {
+    const service = new OidcDiscoveryService(environment);
+    expect(() => service.getTokenEndpoint()).toThrow(
+      'OIDC discovery has not completed yet',
+    );
+  });
+});
diff --git a/backend/libs/auth/src/oidc-discovery.service.ts b/backend/libs/auth/src/oidc-discovery.service.ts
index 43c66f4..bbc4aca 100644
--- a/backend/libs/auth/src/oidc-discovery.service.ts
+++ b/backend/libs/auth/src/oidc-discovery.service.ts
@@ -6,11 +6,13 @@ import type { AppEnvironment } from '../../configuration/src';
 
 interface OidcDiscoveryDocument {
   jwks_uri: string;
+  token_endpoint: string;
 }
 
 @Injectable()
 export class OidcDiscoveryService implements OnModuleInit {
   private verificationKeySet: JWTVerifyGetKey | undefined;
+  private tokenEndpoint: string | undefined;
 
   constructor(
     @Inject(APP_ENVIRONMENT) private readonly environment: AppEnvironment,
@@ -26,6 +28,7 @@ export class OidcDiscoveryService implements OnModuleInit {
     }
     const document = (await response.json()) as OidcDiscoveryDocument;
     this.verificationKeySet = createRemoteJWKSet(new URL(document.jwks_uri));
+    this.tokenEndpoint = document.token_endpoint;
   }
 
   getIssuer(): string {
@@ -42,4 +45,11 @@ export class OidcDiscoveryService implements OnModuleInit {
     }
     return this.verificationKeySet;
   }
+
+  getTokenEndpoint(): string {
+    if (!this.tokenEndpoint) {
+      throw new Error('OIDC discovery has not completed yet');
+    }
+    return this.tokenEndpoint;
+  }
 }
diff --git a/backend/libs/auth/src/token-exchange.service.spec.ts b/backend/libs/auth/src/token-exchange.service.spec.ts
new file mode 100644
index 0000000..cd11491
--- /dev/null
+++ b/backend/libs/auth/src/token-exchange.service.spec.ts
@@ -0,0 +1,110 @@
+import { BadRequestException } from '@nestjs/common';
+import { TokenExchangeService } from './token-exchange.service';
+import type { AppEnvironment } from '../../configuration/src';
+
+describe('TokenExchangeService.exchangeAuthorizationCode', () => {
+  const environment: AppEnvironment = {
+    databaseUrl: 'postgresql://u:p@postgres:5432/db',
+    redisUrl: 'redis://redis:6379',
+    oidcIssuer: 'https://idp.example.test',
+    oidcAudience: 'client-1',
+    oidcClientId: 'client-1',
+    oidcClientSecret: 'super-secret',
+    appVersion: 'dev',
+    teamCityBuildNumber: 'local',
+    sourceRevision: 'local',
+  };
+
+  function fakeDiscovery(
+    tokenEndpoint = 'https://idp.example.test/oidc/token',
+  ) {
+    return { getTokenEndpoint: jest.fn().mockReturnValue(tokenEndpoint) };
+  }
+
+  it('posts a client-secret-authenticated request and returns only the safe fields', async () => {
+    const fetchMock = jest.fn().mockResolvedValue({
+      ok: true,
+      json: () =>
+        Promise.resolve({
+          access_token: 'at-1',
+          expires_in: 3600,
+          refresh_token: 'rt-1',
+          id_token: 'idt-1',
+        }),
+    });
+    (globalThis as { fetch: typeof fetch }).fetch = fetchMock as never;
+
+    const service = new TokenExchangeService(
+      environment,
+      fakeDiscovery() as never,
+    );
+    const result = await service.exchangeAuthorizationCode({
+      code: 'auth-code-1',
+      codeVerifier: 'verifier-1',
+      redirectUri: 'http://localhost:4200/auth/callback',
+    });
+
+    expect(result).toEqual({ accessToken: 'at-1', expiresIn: 3600 });
+
+    const [url, init] = fetchMock.mock.calls[0] as [string, RequestInit];
+    expect(url).toBe('https://idp.example.test/oidc/token');
+    const body = new URLSearchParams(init.body as string);
+    expect(body.get('grant_type')).toBe('authorization_code');
+    expect(body.get('client_id')).toBe('client-1');
+    expect(body.get('client_secret')).toBe('super-secret');
+    expect(body.get('code')).toBe('auth-code-1');
+    expect(body.get('code_verifier')).toBe('verifier-1');
+    expect(body.get('redirect_uri')).toBe(
+      'http://localhost:4200/auth/callback',
+    );
+  });
+
+  it('never leaks the refresh_token or id_token to the caller', async () => {
+    const fetchMock = jest.fn().mockResolvedValue({
+      ok: true,
+      json: () =>
+        Promise.resolve({
+          access_token: 'at-1',
+          expires_in: 3600,
+          refresh_token: 'rt-1',
+          id_token: 'idt-1',
+        }),
+    });
+    (globalThis as { fetch: typeof fetch }).fetch = fetchMock as never;
+
+    const service = new TokenExchangeService(
+      environment,
+      fakeDiscovery() as never,
+    );
+    const result = await service.exchangeAuthorizationCode({
+      code: 'auth-code-1',
+      codeVerifier: 'verifier-1',
+      redirectUri: 'http://localhost:4200/auth/callback',
+    });
+
+    expect(result).not.toHaveProperty('refreshToken');
+    expect(result).not.toHaveProperty('idToken');
+  });
+
+  it('rejects with BadRequestException when the identity provider rejects the code', async () => {
+    const fetchMock = jest.fn().mockResolvedValue({
+      ok: false,
+      status: 400,
+      json: () => Promise.resolve({ error: 'invalid_grant' }),
+    });
+    (globalThis as { fetch: typeof fetch }).fetch = fetchMock as never;
+
+    const service = new TokenExchangeService(
+      environment,
+      fakeDiscovery() as never,
+    );
+
+    await expect(
+      service.exchangeAuthorizationCode({
+        code: 'bad-code',
+        codeVerifier: 'verifier-1',
+        redirectUri: 'http://localhost:4200/auth/callback',
+      }),
+    ).rejects.toThrow(BadRequestException);
+  });
+});
diff --git a/backend/libs/auth/src/token-exchange.service.ts b/backend/libs/auth/src/token-exchange.service.ts
new file mode 100644
index 0000000..6909519
--- /dev/null
+++ b/backend/libs/auth/src/token-exchange.service.ts
@@ -0,0 +1,68 @@
+import { BadRequestException, Inject, Injectable } from '@nestjs/common';
+import { APP_ENVIRONMENT } from '../../configuration/src';
+import type { AppEnvironment } from '../../configuration/src';
+import { OidcDiscoveryService } from './oidc-discovery.service';
+
+export interface AuthorizationCodeExchangeRequest {
+  code: string;
+  codeVerifier: string;
+  redirectUri: string;
+}
+
+export interface AuthorizationCodeExchangeResult {
+  accessToken: string;
+  expiresIn: number;
+}
+
+interface TokenEndpointResponse {
+  access_token: string;
+  expires_in: number;
+  refresh_token?: string;
+  id_token?: string;
+}
+
+/**
+ * Exchanges an OIDC authorization code for tokens on behalf of the (confidential,
+ * client-secret-bearing) SPA client. The secret never reaches the browser: the
+ * frontend performs the Authorization Code + PKCE redirect itself, then hands the
+ * resulting code + PKCE verifier to this service, which is the only place the
+ * client secret is used.
+ */
+@Injectable()
+export class TokenExchangeService {
+  constructor(
+    @Inject(APP_ENVIRONMENT) private readonly environment: AppEnvironment,
+    private readonly discovery: OidcDiscoveryService,
+  ) {}
+
+  async exchangeAuthorizationCode(
+    request: AuthorizationCodeExchangeRequest,
+  ): Promise<AuthorizationCodeExchangeResult> {
+    const body = new URLSearchParams({
+      grant_type: 'authorization_code',
+      client_id: this.environment.oidcClientId,
+      client_secret: this.environment.oidcClientSecret,
+      code: request.code,
+      code_verifier: request.codeVerifier,
+      redirect_uri: request.redirectUri,
+    });
+
+    const response = await fetch(this.discovery.getTokenEndpoint(), {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+      body: body.toString(),
+    });
+
+    if (!response.ok) {
+      throw new BadRequestException(
+        'The identity provider rejected the authorization code',
+      );
+    }
+
+    const tokenResponse = (await response.json()) as TokenEndpointResponse;
+    return {
+      accessToken: tokenResponse.access_token,
+      expiresIn: tokenResponse.expires_in,
+    };
+  }
+}
diff --git a/backend/libs/configuration/src/environment.spec.ts b/backend/libs/configuration/src/environment.spec.ts
index 6d38d48..962e6c5 100644
--- a/backend/libs/configuration/src/environment.spec.ts
+++ b/backend/libs/configuration/src/environment.spec.ts
@@ -12,6 +12,8 @@ describe('loadEnvironment', () => {
         REDIS_URL: 'redis://redis:6379',
         OIDC_ISSUER: 'https://idp.example.test/',
         OIDC_AUDIENCE: 'travel-planner-api',
+        OIDC_CLIENT_ID: 'test-client',
+        OIDC_CLIENT_SECRET: 'test-secret',
         APP_VERSION: '1.2.3',
         TEAMCITY_BUILD_NUMBER: '42',
         SOURCE_REVISION: 'abc123',
@@ -21,6 +23,8 @@ describe('loadEnvironment', () => {
       redisUrl: 'redis://redis:6379',
       oidcIssuer: 'https://idp.example.test/',
       oidcAudience: 'travel-planner-api',
+      oidcClientId: 'test-client',
+      oidcClientSecret: 'test-secret',
       appVersion: '1.2.3',
       teamCityBuildNumber: '42',
       sourceRevision: 'abc123',
diff --git a/backend/libs/configuration/src/environment.ts b/backend/libs/configuration/src/environment.ts
index 8324a55..763d825 100644
--- a/backend/libs/configuration/src/environment.ts
+++ b/backend/libs/configuration/src/environment.ts
@@ -3,6 +3,8 @@ export interface AppEnvironment {
   redisUrl: string;
   oidcIssuer: string;
   oidcAudience: string;
+  oidcClientId: string;
+  oidcClientSecret: string;
   appVersion: string;
   teamCityBuildNumber: string;
   sourceRevision: string;
@@ -20,6 +22,8 @@ export function loadEnvironment(env: NodeJS.ProcessEnv): AppEnvironment {
     redisUrl: required(env, 'REDIS_URL'),
     oidcIssuer: required(env, 'OIDC_ISSUER'),
     oidcAudience: required(env, 'OIDC_AUDIENCE'),
+    oidcClientId: required(env, 'OIDC_CLIENT_ID'),
+    oidcClientSecret: required(env, 'OIDC_CLIENT_SECRET'),
     appVersion: env.APP_VERSION?.trim() || 'dev',
     teamCityBuildNumber: env.TEAMCITY_BUILD_NUMBER?.trim() || 'local',
     sourceRevision: env.SOURCE_REVISION?.trim() || 'local',
diff --git a/backend/test/setup-env.ts b/backend/test/setup-env.ts
index 560f4ec..63c65d7 100644
--- a/backend/test/setup-env.ts
+++ b/backend/test/setup-env.ts
@@ -2,3 +2,5 @@ process.env.DATABASE_URL ??= 'postgresql://test:test@localhost:5432/test';
 process.env.REDIS_URL ??= 'redis://localhost:6379';
 process.env.OIDC_ISSUER ??= 'https://idp.example.test/';
 process.env.OIDC_AUDIENCE ??= 'travel-planner-api';
+process.env.OIDC_CLIENT_ID ??= 'test-client';
+process.env.OIDC_CLIENT_SECRET ??= 'test-secret';
diff --git a/compose.yml b/compose.yml
index 2f8d556..e83d9ba 100644
--- a/compose.yml
+++ b/compose.yml
@@ -30,6 +30,8 @@ services:
       REDIS_URL: "redis://redis:6379"
       OIDC_ISSUER: "${OIDC_ISSUER}"
       OIDC_AUDIENCE: "${OIDC_AUDIENCE}"
+      OIDC_CLIENT_ID: "${OIDC_CLIENT_ID}"
+      OIDC_CLIENT_SECRET: "${OIDC_CLIENT_SECRET}"
       APP_VERSION: "${APP_VERSION:-dev}"
       TEAMCITY_BUILD_NUMBER: "${TEAMCITY_BUILD_NUMBER:-local}"
       SOURCE_REVISION: "${SOURCE_REVISION:-local}"
@@ -57,6 +59,8 @@ services:
       REDIS_URL: "redis://redis:6379"
       OIDC_ISSUER: "${OIDC_ISSUER}"
       OIDC_AUDIENCE: "${OIDC_AUDIENCE}"
+      OIDC_CLIENT_ID: "${OIDC_CLIENT_ID}"
+      OIDC_CLIENT_SECRET: "${OIDC_CLIENT_SECRET}"
       APP_VERSION: "${APP_VERSION:-dev}"
       TEAMCITY_BUILD_NUMBER: "${TEAMCITY_BUILD_NUMBER:-local}"
       SOURCE_REVISION: "${SOURCE_REVISION:-local}"
diff --git a/docs/superpowers/plans/travel-planner-phase-02-users-oidc-trips-plan.md b/docs/superpowers/plans/travel-planner-phase-02-users-oidc-trips-plan.md
index ed5e3f2..e006191 100644
--- a/docs/superpowers/plans/travel-planner-phase-02-users-oidc-trips-plan.md
+++ b/docs/superpowers/plans/travel-planner-phase-02-users-oidc-trips-plan.md
@@ -1325,3 +1325,18 @@ Do not start any of the following during this phase; each belongs to a later, ex
 - Payment/booking automation (permanent non-goal).
 
 Phase 03 begins only after the Phase 02 acceptance checklist is reviewed and green.
+
+---
+
+## Addendum: Confidential IdP Client Requires Backend Token Exchange (2026-08-17)
+
+The plan's Task 10 assumed a public, PKCE-only SPA client and used `oidc-client-ts` to perform the full Authorization Code + PKCE token exchange directly in the browser. During manual end-to-end testing against the actual target IdP (`https://auth.forgecore.work`), it turned out the provisioned client is **confidential** (it has a client secret) rather than public. A client secret must never be shipped in a browser bundle, so this required a real, user-confirmed architecture change rather than a workaround:
+
+- The frontend still performs the Authorization Code + PKCE redirect itself (hand-rolled PKCE generation in `frontend/src/app/auth/pkce.ts`; `oidc-client-ts` was removed as a dependency since its callback handling assumes a direct-to-IdP token exchange that doesn't fit this model).
+- The resulting authorization `code` and PKCE `code_verifier` are POSTed to a new, intentionally unauthenticated backend endpoint, `POST /api/v1/auth/session` (`AuthSessionController` → `TokenExchangeService`), which performs the code-for-tokens exchange using `OIDC_CLIENT_SECRET` server-side and returns only `{ accessToken, expiresIn }` — `refresh_token`/`id_token` are deliberately never forwarded to the frontend.
+- New required backend env vars: `OIDC_CLIENT_ID`, `OIDC_CLIENT_SECRET` (in addition to the already-planned `OIDC_ISSUER`/`OIDC_AUDIENCE`).
+- `OIDC_AUDIENCE` is operationally set equal to `OIDC_CLIENT_ID` for this IdP, since it does not issue a separate API-resource audience; no code change was needed for this, only a configuration convention.
+- `OidcDiscoveryService` now also captures `token_endpoint` (in addition to `jwks_uri`), needed for the backend-side token exchange.
+- A local dev proxy (`frontend/proxy.conf.json`, wired into `angular.json`'s `serve` target) forwards `/api/*` and `/health/*` from the Angular dev server to the API, avoiding a need for CORS configuration in local development (production already avoids CORS entirely since `edge` serves both origins).
+
+This is a deployment-specific IdP constraint, not a general Travel Planner requirement — a future public-client IdP could skip the backend proxy — but the BFF pattern is what ships today since it is what the actual configured IdP requires.
diff --git a/frontend/angular.json b/frontend/angular.json
index 286f0bc..d6267a9 100644
--- a/frontend/angular.json
+++ b/frontend/angular.json
@@ -64,6 +64,9 @@
         },
         "serve": {
           "builder": "@angular/build:dev-server",
+          "options": {
+            "proxyConfig": "proxy.conf.json"
+          },
           "configurations": {
             "production": {
               "buildTarget": "frontend:build:production"
diff --git a/frontend/package.json b/frontend/package.json
index b4716ea..5344ef4 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -17,7 +17,6 @@
     "@angular/platform-browser": "^21.2.0",
     "@angular/router": "^21.2.0",
     "@angular/service-worker": "^21.2.0",
-    "oidc-client-ts": "^3.5.0",
     "rxjs": "~7.8.0",
     "tslib": "^2.3.0"
   },
diff --git a/frontend/proxy.conf.json b/frontend/proxy.conf.json
new file mode 100644
index 0000000..76ed92e
--- /dev/null
+++ b/frontend/proxy.conf.json
@@ -0,0 +1,4 @@
+{
+  "/api": { "target": "http://localhost:3000", "secure": false },
+  "/health": { "target": "http://localhost:3000", "secure": false }
+}
diff --git a/frontend/src/app/auth/auth.service.spec.ts b/frontend/src/app/auth/auth.service.spec.ts
index 40afd2e..a7e0459 100644
--- a/frontend/src/app/auth/auth.service.spec.ts
+++ b/frontend/src/app/auth/auth.service.spec.ts
@@ -1,11 +1,87 @@
 import { TestBed } from '@angular/core/testing';
-import { describe, expect, it } from 'vitest';
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
 import { AuthService } from './auth.service';
 
 describe('AuthService', () => {
-  it('starts unauthenticated when no OIDC user is stored', async () => {
+  beforeEach(() => {
+    sessionStorage.clear();
+  });
+
+  afterEach(() => {
+    vi.unstubAllGlobals();
+  });
+
+  it('starts unauthenticated when no session is stored', () => {
     const service = TestBed.inject(AuthService);
-    await Promise.resolve();
     expect(service.isAuthenticated()).toBe(false);
   });
+
+  it('starts authenticated when a non-expired access token is already stored', () => {
+    sessionStorage.setItem('auth.accessToken', 'stored-token');
+    sessionStorage.setItem('auth.expiresAt', String(Date.now() + 60_000));
+    const service = TestBed.inject(AuthService);
+    expect(service.isAuthenticated()).toBe(true);
+  });
+
+  it('login() persists a PKCE verifier and state before redirecting', async () => {
+    const fetchMock = vi.fn().mockResolvedValue({
+      json: () => Promise.resolve({ authorization_endpoint: 'https://idp.example.test/oidc/auth' }),
+    });
+    vi.stubGlobal('fetch', fetchMock);
+    vi.stubGlobal('location', { ...window.location, href: '' });
+
+    const service = TestBed.inject(AuthService);
+    await service.login();
+
+    expect(sessionStorage.getItem('auth.codeVerifier')).toBeTruthy();
+    expect(sessionStorage.getItem('auth.state')).toBeTruthy();
+    expect(window.location.href).toContain('https://idp.example.test/oidc/auth?');
+    expect(window.location.href).toContain('code_challenge_method=S256');
+  });
+
+  it('completeLogin() rejects a state that does not match the one stored before redirecting', async () => {
+    sessionStorage.setItem('auth.codeVerifier', 'verifier-1');
+    sessionStorage.setItem('auth.state', 'expected-state');
+    vi.stubGlobal('location', { ...window.location, search: '?code=abc&state=wrong-state' });
+
+    const service = TestBed.inject(AuthService);
+    await expect(service.completeLogin()).rejects.toThrow();
+  });
+
+  it('completeLogin() exchanges the code via the backend and stores the resulting access token', async () => {
+    sessionStorage.setItem('auth.codeVerifier', 'verifier-1');
+    sessionStorage.setItem('auth.state', 'state-1');
+    vi.stubGlobal('location', { ...window.location, search: '?code=abc&state=state-1' });
+
+    const fetchMock = vi.fn().mockResolvedValue({
+      ok: true,
+      json: () => Promise.resolve({ accessToken: 'at-1', expiresIn: 3600 }),
+    });
+    vi.stubGlobal('fetch', fetchMock);
+
+    const service = TestBed.inject(AuthService);
+    await service.completeLogin();
+
+    expect(service.isAuthenticated()).toBe(true);
+    await expect(service.getAccessToken()).resolves.toBe('at-1');
+    expect(sessionStorage.getItem('auth.codeVerifier')).toBeNull();
+  });
+
+  it('logout() clears the stored session', () => {
+    sessionStorage.setItem('auth.accessToken', 'at-1');
+    sessionStorage.setItem('auth.expiresAt', String(Date.now() + 60_000));
+    const service = TestBed.inject(AuthService);
+
+    service.logout();
+
+    expect(service.isAuthenticated()).toBe(false);
+  });
+
+  it('getAccessToken() returns undefined once the token has expired', async () => {
+    sessionStorage.setItem('auth.accessToken', 'at-1');
+    sessionStorage.setItem('auth.expiresAt', String(Date.now() - 1000));
+    const service = TestBed.inject(AuthService);
+
+    await expect(service.getAccessToken()).resolves.toBeUndefined();
+  });
 });
diff --git a/frontend/src/app/auth/auth.service.ts b/frontend/src/app/auth/auth.service.ts
index 2a39293..c66a202 100644
--- a/frontend/src/app/auth/auth.service.ts
+++ b/frontend/src/app/auth/auth.service.ts
@@ -1,39 +1,103 @@
 import { Injectable, signal } from '@angular/core';
-import { UserManager } from 'oidc-client-ts';
 import { environment } from '../../environments/environment';
+import { generateCodeChallenge, generateRandomString } from './pkce';
 
+const ACCESS_TOKEN_KEY = 'auth.accessToken';
+const EXPIRES_AT_KEY = 'auth.expiresAt';
+const CODE_VERIFIER_KEY = 'auth.codeVerifier';
+const STATE_KEY = 'auth.state';
+
+interface DiscoveryDocument {
+  authorization_endpoint: string;
+}
+
+interface SessionResponse {
+  accessToken: string;
+  expiresIn: number;
+}
+
+/**
+ * The IdP client backing this app is confidential (holds a client secret), so
+ * the authorization-code-for-tokens exchange must happen server-side — see
+ * `POST /api/v1/auth/session`. This service only performs the browser-side
+ * Authorization Code + PKCE redirect and hands the resulting code + PKCE
+ * verifier to the backend; it never sees or stores the client secret.
+ */
 @Injectable({ providedIn: 'root' })
 export class AuthService {
-  private readonly userManager = new UserManager({
-    authority: environment.oidc.issuer,
-    client_id: environment.oidc.clientId,
-    redirect_uri: environment.oidc.redirectUri,
-    scope: environment.oidc.scope,
-    response_type: 'code',
-  });
+  private discoveryPromise: Promise<DiscoveryDocument> | undefined;
 
-  readonly isAuthenticated = signal(false);
+  readonly isAuthenticated = signal(this.hasValidAccessToken());
 
-  constructor() {
-    this.userManager.events.addUserLoaded(() => this.isAuthenticated.set(true));
-    this.userManager.events.addUserUnloaded(() => this.isAuthenticated.set(false));
-    void this.userManager.getUser().then((user) => this.isAuthenticated.set(!!user && !user.expired));
+  private hasValidAccessToken(): boolean {
+    const expiresAt = Number(sessionStorage.getItem(EXPIRES_AT_KEY) ?? 0);
+    return !!sessionStorage.getItem(ACCESS_TOKEN_KEY) && Date.now() < expiresAt;
   }
 
-  login(): Promise<void> {
-    return this.userManager.signinRedirect();
+  private discover(): Promise<DiscoveryDocument> {
+    if (!this.discoveryPromise) {
+      const issuer = environment.oidc.issuer.replace(/\/$/, '');
+      this.discoveryPromise = fetch(`${issuer}/.well-known/openid-configuration`).then((response) => response.json());
+    }
+    return this.discoveryPromise;
+  }
+
+  async login(): Promise<void> {
+    const codeVerifier = generateRandomString();
+    const state = generateRandomString();
+    const codeChallenge = await generateCodeChallenge(codeVerifier);
+    sessionStorage.setItem(CODE_VERIFIER_KEY, codeVerifier);
+    sessionStorage.setItem(STATE_KEY, state);
+
+    const discovery = await this.discover();
+    const url = new URL(discovery.authorization_endpoint);
+    url.searchParams.set('response_type', 'code');
+    url.searchParams.set('client_id', environment.oidc.clientId);
+    url.searchParams.set('redirect_uri', environment.oidc.redirectUri);
+    url.searchParams.set('scope', environment.oidc.scope);
+    url.searchParams.set('state', state);
+    url.searchParams.set('code_challenge', codeChallenge);
+    url.searchParams.set('code_challenge_method', 'S256');
+
+    window.location.href = url.toString();
   }
 
   async completeLogin(): Promise<void> {
-    await this.userManager.signinRedirectCallback();
+    const params = new URLSearchParams(window.location.search);
+    const code = params.get('code');
+    const state = params.get('state');
+    const codeVerifier = sessionStorage.getItem(CODE_VERIFIER_KEY);
+    const expectedState = sessionStorage.getItem(STATE_KEY);
+
+    if (!code || !state || !codeVerifier || state !== expectedState) {
+      throw new Error('Invalid or missing OIDC callback parameters');
+    }
+
+    const response = await fetch(`${environment.apiBaseUrl}/auth/session`, {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({ code, codeVerifier, redirectUri: environment.oidc.redirectUri }),
+    });
+
+    if (!response.ok) {
+      throw new Error('Failed to exchange the authorization code for a session');
+    }
+
+    const session = (await response.json()) as SessionResponse;
+    sessionStorage.setItem(ACCESS_TOKEN_KEY, session.accessToken);
+    sessionStorage.setItem(EXPIRES_AT_KEY, String(Date.now() + session.expiresIn * 1000));
+    sessionStorage.removeItem(CODE_VERIFIER_KEY);
+    sessionStorage.removeItem(STATE_KEY);
+    this.isAuthenticated.set(true);
   }
 
-  logout(): Promise<void> {
-    return this.userManager.signoutRedirect();
+  logout(): void {
+    sessionStorage.removeItem(ACCESS_TOKEN_KEY);
+    sessionStorage.removeItem(EXPIRES_AT_KEY);
+    this.isAuthenticated.set(false);
   }
 
   async getAccessToken(): Promise<string | undefined> {
-    const user = await this.userManager.getUser();
-    return user && !user.expired ? user.access_token : undefined;
+    return this.hasValidAccessToken() ? (sessionStorage.getItem(ACCESS_TOKEN_KEY) ?? undefined) : undefined;
   }
 }
diff --git a/frontend/src/app/auth/pkce.spec.ts b/frontend/src/app/auth/pkce.spec.ts
new file mode 100644
index 0000000..856aa24
--- /dev/null
+++ b/frontend/src/app/auth/pkce.spec.ts
@@ -0,0 +1,21 @@
+import { describe, expect, it } from 'vitest';
+import { generateCodeChallenge, generateRandomString } from './pkce';
+
+describe('pkce', () => {
+  it('computes the RFC 7636 Appendix B S256 test vector', async () => {
+    // https://datatracker.ietf.org/doc/html/rfc7636#appendix-B
+    const codeVerifier = 'dBjftJeZ4CVP-mB92K27uhbUJU1p1r_wW1gFWFOEjXk';
+    const challenge = await generateCodeChallenge(codeVerifier);
+    expect(challenge).toBe('E9Melhoa2OwvFrEMTJguCHaoeK1t8URWbuGJSstw-cM');
+  });
+
+  it('generates a URL-safe random string of the requested length family', () => {
+    const value = generateRandomString();
+    expect(value).toMatch(/^[A-Za-z0-9_-]+$/);
+    expect(value.length).toBeGreaterThanOrEqual(43);
+  });
+
+  it('generates different values on each call', () => {
+    expect(generateRandomString()).not.toBe(generateRandomString());
+  });
+});
diff --git a/frontend/src/app/auth/pkce.ts b/frontend/src/app/auth/pkce.ts
new file mode 100644
index 0000000..69beb19
--- /dev/null
+++ b/frontend/src/app/auth/pkce.ts
@@ -0,0 +1,16 @@
+function base64UrlEncode(bytes: Uint8Array): string {
+  let binary = '';
+  for (const byte of bytes) binary += String.fromCharCode(byte);
+  return btoa(binary).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
+}
+
+export function generateRandomString(byteLength = 32): string {
+  const bytes = new Uint8Array(byteLength);
+  crypto.getRandomValues(bytes);
+  return base64UrlEncode(bytes);
+}
+
+export async function generateCodeChallenge(codeVerifier: string): Promise<string> {
+  const digest = await crypto.subtle.digest('SHA-256', new TextEncoder().encode(codeVerifier));
+  return base64UrlEncode(new Uint8Array(digest));
+}
diff --git a/frontend/src/environments/environment.ts b/frontend/src/environments/environment.ts
index 931e419..7ee5791 100644
--- a/frontend/src/environments/environment.ts
+++ b/frontend/src/environments/environment.ts
@@ -2,8 +2,8 @@ export const environment = {
   production: false,
   apiBaseUrl: '/api/v1',
   oidc: {
-    issuer: 'https://idp.example.invalid/realms/travel-planner',
-    clientId: 'travel-planner-web',
+    issuer: 'https://auth.forgecore.work',
+    clientId: 'client_a297fd8d9c1f47a79d3600ea0c96984',
     redirectUri: `${window.location.origin}/auth/callback`,
     scope: 'openid profile email',
   },
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 0293a9f..69b7404 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -141,9 +141,6 @@ importers:
       '@angular/service-worker':
         specifier: ^21.2.0
         version: 21.2.20(@angular/core@21.2.20(@angular/compiler@21.2.20)(rxjs@7.8.2))(rxjs@7.8.2)
-      oidc-client-ts:
-        specifier: ^3.5.0
-        version: 3.5.0
       rxjs:
         specifier: ~7.8.0
         version: 7.8.2
@@ -3537,10 +3534,6 @@ packages:
     resolution: {integrity: sha512-POQXvpdL69+CluYsillJ7SUhKvytYjW9vG/GKpnf+xP8UWgYEM/RaMzHHofbALDiKbbP1W8UEYmgGl39WkPZsg==}
     engines: {'0': node >= 0.2.0}
 
-  jwt-decode@4.0.0:
-    resolution: {integrity: sha512-+KJGIyHgkGuIq3IEBNftfhW/LfWhXUIY6OmyVWjliu5KH1y0fw7VQ8YndE2O4qZdMSd9SqbnC8GOcZEy0Om7sA==}
-    engines: {node: '>=18'}
-
   keyv@4.5.4:
     resolution: {integrity: sha512-oxVHkHR/EJf2CNXnWxRLW6mg7JyCCUcG0DtEGmL2ctUo1PNTin1PUil+r/+4r5MpVgC/fn1kjsx7mjSujKqIpw==}
 
@@ -3876,10 +3869,6 @@ packages:
     resolution: {integrity: sha512-4a+OsYv9UktOJKE+l1A4OufDgdRF9PifWj+tJnHURo/P+WOxpG4GzUFL9qCalmWauao6ogiG+QvnCovwPoyAWA==}
     engines: {node: '>=12.20.0'}
 
-  oidc-client-ts@3.5.0:
-    resolution: {integrity: sha512-l2q8l9CTCTOlbX+AnK4p3M+4CEpKpyQhle6blQkdFhm0IsBqsxm15bYaSa11G7pWdsYr6epdsRZxJpCyCRbT8A==}
-    engines: {node: '>=18'}
-
   on-finished@2.4.1:
     resolution: {integrity: sha512-oVlzkg3ENAhCk2zdv7IJwd/QUD4z2RxRwpkcGY8psCVcCYZNq4wYnVWALHM+brtuJjePWiYF/ClmuDr8Ch5+kg==}
     engines: {node: '>= 0.8'}
@@ -8690,8 +8679,6 @@ snapshots:
 
   jsonparse@1.3.1: {}
 
-  jwt-decode@4.0.0: {}
-
   keyv@4.5.4:
     dependencies:
       json-buffer: 3.0.1
@@ -9041,10 +9028,6 @@ snapshots:
 
   obug@2.1.4: {}
 
-  oidc-client-ts@3.5.0:
-    dependencies:
-      jwt-decode: 4.0.0
-
   on-finished@2.4.1:
     dependencies:
       ee-first: 1.1.1