Add unit test for external browser auth with Azure client ID

Add test to verify that ExternalBrowserCredentialsProvider correctly
resolves and passes Azure OIDC endpoints to the OAuthClient when using
Azure client ID authentication.

The test:
- Mocks external browser authentication flow with Azure credentials
- Captures the OpenIDConnectEndpoints passed to performBrowserAuth
- Verifies the endpoints match the expected Azure OIDC URLs

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: hectorcast-db

databricks-sdk-java/src/test/java/com/databricks/sdk/core/oauth/ExternalBrowserCredentialsProviderTest.java

@@ -660,4 +660,92 @@ void addOfflineAccessScopeWhenDisableOauthRefreshTokenIsFalse() {
     assertTrue(scopes.contains("offline_access"));
     assertTrue(scopes.contains("my-test-scope"));
   }
+
+  @Test
+  void externalBrowserAuthWithAzureClientIdTest() throws IOException {
+    // Create mock HTTP client
+    HttpClient mockHttpClient = Mockito.mock(HttpClient.class);
+
+    // Mock token cache
+    TokenCache mockTokenCache = Mockito.mock(TokenCache.class);
+    Mockito.doReturn(null).when(mockTokenCache).load();
+
+    // Create valid token for browser auth
+    Token browserAuthToken =
+        new Token(
+            "azure_access_token",
+            "Bearer",
+            "azure_refresh_token",
+            Instant.now().plusSeconds(3600));
+
+    // Create token source
+    SessionCredentialsTokenSource browserAuthTokenSource =
+        new SessionCredentialsTokenSource(
+            browserAuthToken,
+            mockHttpClient,
+            "https://test.azuredatabricks.net/oidc/v1/token",
+            "test-azure-client-id",
+            null,
+            Optional.empty(),
+            Optional.empty());
+
+    CachedTokenSource cachedTokenSource =
+        new CachedTokenSource.Builder(browserAuthTokenSource).setToken(browserAuthToken).build();
+
+    // Create Azure config with Azure client ID
+    DatabricksConfig config =
+        new DatabricksConfig()
+            .setAuthType("external-browser")
+            .setHost("https://test.azuredatabricks.net")
+            .setAzureClientId("test-azure-client-id")
+            .setHttpClient(mockHttpClient);
+
+    // Create provider and mock browser auth
+    ExternalBrowserCredentialsProvider provider =
+        Mockito.spy(new ExternalBrowserCredentialsProvider(mockTokenCache));
+    Mockito.doReturn(cachedTokenSource)
+        .when(provider)
+        .performBrowserAuth(
+            any(DatabricksConfig.class),
+            any(),
+            any(),
+            any(TokenCache.class),
+            any(OpenIDConnectEndpoints.class));
+
+    // Spy on config to inject OIDC endpoints
+    OpenIDConnectEndpoints endpoints =
+        new OpenIDConnectEndpoints(
+            "https://test.azuredatabricks.net/oidc/v1/token",
+            "https://test.azuredatabricks.net/oidc/v1/authorize");
+    DatabricksConfig spyConfig = Mockito.spy(config);
+    Mockito.doReturn(endpoints).when(spyConfig).getOidcEndpoints();
+
+    // Configure provider
+    HeaderFactory headerFactory = provider.configure(spyConfig);
+    assertNotNull(headerFactory);
+
+    // Verify headers contain the Azure token
+    Map<String, String> headers = headerFactory.headers();
+    assertEquals("Bearer azure_access_token", headers.get("Authorization"));
+
+    // Capture and verify the OpenIDConnectEndpoints passed to performBrowserAuth
+    ArgumentCaptor<OpenIDConnectEndpoints> endpointsCaptor =
+        ArgumentCaptor.forClass(OpenIDConnectEndpoints.class);
+    Mockito.verify(provider, Mockito.times(1))
+        .performBrowserAuth(
+            any(DatabricksConfig.class),
+            any(),
+            any(),
+            any(TokenCache.class),
+            endpointsCaptor.capture());
+
+    // Verify the captured endpoints match what we expect for Azure
+    OpenIDConnectEndpoints capturedEndpoints = endpointsCaptor.getValue();
+    assertNotNull(capturedEndpoints);
+    assertEquals("https://test.azuredatabricks.net/oidc/v1/token", capturedEndpoints.getTokenEndpoint());
+    assertEquals("https://test.azuredatabricks.net/oidc/v1/authorize", capturedEndpoints.getAuthorizationEndpoint());
+
+    // Verify token was saved
+    Mockito.verify(mockTokenCache, Mockito.times(1)).save(any(Token.class));
+  }
 }