feat: add loginWithCustomTokenExchange method

Adds `loginWithCustomTokenExchange()` method following the PRD naming convention for Custom Token Exchange operations, implementing the spa-js 2.14.0 feature.

Changes:
- Added `loginWithCustomTokenExchange()` method to AuthService
- Exchanges external tokens and establishes authenticated session
- Bumped @auth0/auth0-spa-js from 2.13.0 to 2.14.0
- Added comprehensive tests (5 new tests)
- Updated EXAMPLES.md with new method usage

Implementation follows RFC 8693 token exchange grant type.

Author: yogeshchoudhary147

EXAMPLES.md

@@ -6,6 +6,7 @@
 - [Display the user profile](#display-the-user-profile)
 - [Protect a route](#protect-a-route)
 - [Call an API](#call-an-api)
+- [Custom token exchange](#custom-token-exchange)
 - [Wrapping the interceptor for granular control](#wrapping-the-interceptor-for-granular-control)
 - [Handling errors](#handling-errors)
 - [Organizations](#organizations)
@@ -291,6 +292,62 @@ AuthModule.forRoot({
 
 You might want to do this in scenarios where you need the token on multiple endpoints, but want to exclude it from only a few other endpoints. Instead of explicitly listing all endpoints that do need a token, a uriMatcher can be used to include all but the few endpoints that do not need a token attached to its requests.
 
+## Custom token exchange
+
+Exchange an external subject token for Auth0 tokens and establish an authenticated session using the token exchange flow (RFC 8693):
+
+```ts
+import { Component } from '@angular/core';
+import { AuthService, CustomTokenExchangeOptions } from '@auth0/auth0-angular';
+
+@Component({
+  selector: 'app-token-exchange',
+  template: `
+    <button (click)="handleExchange()">Exchange Token</button>
+    <div *ngIf="tokens">Token exchange successful!</div>
+    <div *ngIf="error">Error: {{ error }}</div>
+  `,
+})
+export class TokenExchangeComponent {
+  tokens: any = null;
+  error: string | null = null;
+
+  constructor(private auth: AuthService) {}
+
+  handleExchange() {
+    const options: CustomTokenExchangeOptions = {
+      subject_token: 'your-external-token',
+      subject_token_type: 'urn:your-company:legacy-system-token',
+      audience: 'https://api.example.com/',
+      scope: 'openid profile email',
+    };
+
+    this.auth.loginWithCustomTokenExchange(options).subscribe({
+      next: (tokenResponse) => {
+        this.tokens = tokenResponse;
+        this.error = null;
+
+        // Use the returned tokens
+        console.log('Access Token:', tokenResponse.access_token);
+        console.log('ID Token:', tokenResponse.id_token);
+      },
+      error: (err) => {
+        console.error('Token exchange failed:', err);
+        this.error = err.message;
+      },
+    });
+  }
+}
+```
+
+**Important Notes:**
+
+- The `subject_token_type` must be a namespaced URI under your organization's control
+- The external token must be validated in Auth0 Actions using strong cryptographic verification
+- This method implements RFC 8693 token exchange grant type
+- The audience and scope can be provided directly in the options or will fall back to SDK defaults
+- **State Management:** This method updates the SDK's authentication state after a successful exchange, ensuring that `isLoading$`, `isAuthenticated$`, and `user$` observables behave identically to the standard `getAccessTokenSilently()` flow
+
 ## Wrapping the interceptor for granular control
 
 While the `allowedList` configuration and `uriMatcher` provide flexible ways to control which requests receive access tokens, there may be scenarios where you need even more granular control on a per-request basis. For example:

package-lock.json

@@ -32,7 +32,7 @@
     "@angular/platform-browser": "^19.2.18",
     "@angular/platform-browser-dynamic": "^19.2.18",
     "@angular/router": "^19.2.18",
-    "@auth0/auth0-spa-js": "^2.13.1",
+    "@auth0/auth0-spa-js": "^2.14.0",
     "rxjs": "^6.6.7",
     "tslib": "^2.8.1",
     "zone.js": "~0.15.1"

package.json

@@ -77,6 +77,13 @@ describe('AuthService', () => {
       .spyOn(auth0Client, 'getTokenWithPopup')
       .mockResolvedValue('__access_token_from_popup__');
 
+    jest.spyOn(auth0Client, 'loginWithCustomTokenExchange').mockResolvedValue({
+      access_token: '__exchanged_access_token__',
+      id_token: '__exchanged_id_token__',
+      token_type: 'Bearer',
+      expires_in: 86400,
+    });
+
     jest
       .spyOn(auth0Client, 'getDpopNonce')
       .mockResolvedValue('test-nonce-value');
@@ -922,6 +929,107 @@ describe('AuthService', () => {
     });
   });
 
+  describe('loginWithCustomTokenExchange', () => {
+    it('should call the underlying SDK', (done) => {
+      const service = createService();
+      const options = {
+        subject_token: '__test_token__',
+        subject_token_type: 'urn:test:token-type',
+      };
+
+      service
+        .loginWithCustomTokenExchange(options)
+        .subscribe((tokenResponse) => {
+          expect(auth0Client.loginWithCustomTokenExchange).toHaveBeenCalledWith(
+            options
+          );
+          done();
+        });
+    });
+
+    it('should return the token response', (done) => {
+      const service = createService();
+      const options = {
+        subject_token: '__test_token__',
+        subject_token_type: 'urn:test:token-type',
+        scope: 'openid profile email',
+      };
+
+      service
+        .loginWithCustomTokenExchange(options)
+        .subscribe((tokenResponse) => {
+          expect(tokenResponse).toEqual({
+            access_token: '__exchanged_access_token__',
+            id_token: '__exchanged_id_token__',
+            token_type: 'Bearer',
+            expires_in: 86400,
+          });
+          done();
+        });
+    });
+
+    it('should update auth state after successful token exchange', (done) => {
+      const service = createService();
+      const options = {
+        subject_token: '__test_token__',
+        subject_token_type: 'urn:test:token-type',
+      };
+
+      jest.spyOn(authState, 'setAccessToken');
+
+      service.loginWithCustomTokenExchange(options).subscribe(() => {
+        expect(authState.setAccessToken).toHaveBeenCalledWith(
+          '__exchanged_access_token__'
+        );
+        done();
+      });
+    });
+
+    it('should record errors in the error$ observable', (done) => {
+      const errorObj = new Error('Token exchange failed');
+
+      (
+        auth0Client.loginWithCustomTokenExchange as unknown as jest.SpyInstance
+      ).mockRejectedValue(errorObj);
+
+      const service = createService();
+      service
+        .loginWithCustomTokenExchange({
+          subject_token: '__test_token__',
+          subject_token_type: 'urn:test:token-type',
+        })
+        .subscribe({
+          error: () => {},
+        });
+
+      service.error$.subscribe((err: Error) => {
+        expect(err).toBe(errorObj);
+        done();
+      });
+    });
+
+    it('should bubble errors', (done) => {
+      const errorObj = new Error('Token exchange failed');
+
+      (
+        auth0Client.loginWithCustomTokenExchange as unknown as jest.SpyInstance
+      ).mockRejectedValue(errorObj);
+
+      const service = createService();
+      service
+        .loginWithCustomTokenExchange({
+          subject_token: '__test_token__',
+          subject_token_type: 'urn:test:token-type',
+        })
+        .subscribe({
+          error: (err: Error) => {
+            expect(err).toBe(errorObj);
+            done();
+          },
+        });
+    });
+  });
+
   describe('handleRedirectCallback', () => {
     let navigator: AbstractNavigator;
 

projects/auth0-angular/src/lib/auth.service.spec.ts

@@ -13,6 +13,8 @@ import {
   CustomFetchMinimalOutput,
   Fetcher,
   FetcherConfig,
+  CustomTokenExchangeOptions,
+  TokenEndpointResponse,
 } from '@auth0/auth0-spa-js';
 
 import {
@@ -319,6 +321,48 @@ export class AuthService<TAppState extends AppState = AppState>
     );
   }
 
+  /**
+   * ```js
+   * loginWithCustomTokenExchange(options).subscribe(tokenResponse => ...)
+   * ```
+   *
+   * Exchanges an external subject token for Auth0 tokens and establishes an authenticated session.
+   *
+   * This method implements the token exchange grant as specified in RFC 8693.
+   * It performs a token exchange by sending a request to the `/oauth/token` endpoint
+   * with the external token and returns Auth0 tokens (access token, ID token, etc.).
+   *
+   * The request includes the following parameters:
+   * - `grant_type`: Hard-coded to "urn:ietf:params:oauth:grant-type:token-exchange"
+   * - `subject_token`: The external token to be exchanged
+   * - `subject_token_type`: A namespaced URI identifying the token type (must be under your organization's control)
+   * - `audience`: The target audience (falls back to the SDK's default audience if not provided)
+   * - `scope`: Space-separated list of scopes (merged with the SDK's default scopes)
+   *
+   * After a successful token exchange, this method updates the authentication state
+   * to ensure consistency with the standard authentication flows.
+   *
+   * @param options The options required to perform the token exchange
+   * @returns An Observable that emits the token endpoint response containing Auth0 tokens
+   */
+  loginWithCustomTokenExchange(
+    options: CustomTokenExchangeOptions
+  ): Observable<TokenEndpointResponse> {
+    return of(this.auth0Client).pipe(
+      concatMap((client) => client.loginWithCustomTokenExchange(options)),
+      tap((tokenResponse) => {
+        if (tokenResponse.access_token) {
+          this.authState.setAccessToken(tokenResponse.access_token);
+        }
+      }),
+      catchError((error) => {
+        this.authState.setError(error);
+        this.authState.refresh();
+        return throwError(error);
+      })
+    );
+  }
+
   /**
    * ```js
    * handleRedirectCallback(url).subscribe(result => ...)

projects/auth0-angular/src/lib/auth.service.ts

@@ -38,4 +38,6 @@ export {
   FetcherConfig,
   CustomFetchMinimalOutput,
   UseDpopNonceError,
+  CustomTokenExchangeOptions,
+  TokenEndpointResponse,
 } from '@auth0/auth0-spa-js';