feat: Add Token Vault support to the Authentication API

src/main/java/com/auth0/client/auth/AuthAPI.java

@@ -59,6 +59,8 @@ public class AuthAPI {
     private static final String KEY_CLIENT_ASSERTION_TYPE = "client_assertion_type";
     private static final String KEY_SUBJECT_TOKEN = "subject_token";
     private static final String KEY_SUBJECT_TOKEN_TYPE = "subject_token_type";
+    private static final String KEY_REQUESTED_TOKEN_TYPE = "requested_token_type";
+    private static final String KEY_LOGIN_HINT = "login_hint";
     private static final String PATH_OAUTH = "oauth";
     private static final String PATH_TOKEN = "token";
     private static final String PATH_DBCONNECTIONS = "dbconnections";
@@ -840,6 +842,54 @@ public TokenRequest exchangeToken(String subjectToken, String subjectTokenType)
         return request;
     }
 
+    /**
+     * Creates a request to exchange an Auth0 refresh token for a federated identity provider's access token
+     * using the Token Vault grant
+     * {@code urn:auth0:params:oauth:grant-type:token-exchange:federated-connection-access-token}.
+     * The connection must have the token vault enabled, and client authentication
+     * (client secret or client assertion) is required as this must be a private client.
+     * <pre>
+     * {@code
+     * try {
+     *      TokenHolder result = authAPI.getTokenForConnection("google-oauth2", refreshToken, "google-user-id")
+     *          .execute()
+     *          .getBody();
+     *      String federatedAccessToken = result.getAccessToken();
+     * } catch (Auth0Exception e) {
+     *      //Something happened
+     * }
+     * }
+     * </pre>
+     *
+     * @see <a href="https://auth0.com/docs/secure/tokens/token-vault">Token Vault documentation</a>
+     * @param connection the name of the federated connection to obtain an access token for
+     *                   (for example {@code google-oauth2}). Must not be null.
+     * @param refreshToken a valid Auth0 refresh token to exchange. Must not be null.
+     * @param loginHint the user's ID within the identity provider specified by the connection
+     *                  (for example, the Google user ID when the connection is {@code google-oauth2}).
+     *                  May be null, in which case no {@code login_hint} is sent.
+     * @return a Request to configure and execute.
+     */
+    public TokenRequest getTokenForConnection(String connection, String refreshToken, String loginHint) {
+        Asserts.assertNotNull(connection, "connection");
+        Asserts.assertNotNull(refreshToken, "refresh token");
+
+        TokenRequest request = new TokenRequest(client, getTokenUrl());
+        request.addParameter(KEY_CLIENT_ID, clientId);
+        request.addParameter(
+                KEY_GRANT_TYPE, "urn:auth0:params:oauth:grant-type:token-exchange:federated-connection-access-token");
+        request.addParameter(KEY_SUBJECT_TOKEN, refreshToken);
+        request.addParameter(KEY_SUBJECT_TOKEN_TYPE, "urn:ietf:params:oauth:token-type:refresh_token");
+        request.addParameter(
+                KEY_REQUESTED_TOKEN_TYPE, "http://auth0.com/oauth/token-type/federated-connection-access-token");
+        request.addParameter(KEY_CONNECTION, connection);
+        if (loginHint != null) {
+            request.addParameter(KEY_LOGIN_HINT, loginHint);
+        }
+        addClientAuthentication(request, true);
+        return request;
+    }
+
     /**
      * Creates a request to revoke an existing Refresh Token.
      * Confidential clients (Regular Web Apps) <strong>must</strong> have a client secret configured on this {@code AuthAPI} instance.

src/test/java/com/auth0/client/auth/AuthAPITest.java

@@ -1035,6 +1035,82 @@ public void shouldCreateTokenExchangeRequestWithClientAssertion() throws Excepti
         assertThat(response.getAccessToken(), not(emptyOrNullString()));
     }
 
+    // Token Vault - Federated Connection Access Token
+
+    @Test
+    public void shouldThrowOnGetTokenForConnectionWithNullConnection() {
+        verifyThrows(
+                IllegalArgumentException.class,
+                () -> api.getTokenForConnection(null, "test-refresh-token", null),
+                "'connection' cannot be null!");
+    }
+
+    @Test
+    public void shouldThrowOnGetTokenForConnectionWithNullRefreshToken() {
+        verifyThrows(
+                IllegalArgumentException.class,
+                () -> api.getTokenForConnection("google-oauth2", null, null),
+                "'refresh token' cannot be null!");
+    }
+
+    @Test
+    public void shouldCreateGetTokenForConnectionRequest() throws Exception {
+        TokenRequest request = api.getTokenForConnection("google-oauth2", "test-refresh-token", null);
+        assertThat(request, is(notNullValue()));
+
+        server.jsonResponse(AUTH_TOKENS, 200);
+        TokenHolder response = request.execute().getBody();
+        RecordedRequest recordedRequest = server.takeRequest();
+
+        assertThat(recordedRequest, hasMethodAndPath(HttpMethod.POST, "/oauth/token"));
+        assertThat(recordedRequest, hasHeader("Content-Type", "application/json"));
+
+        Map<String, Object> body = bodyFromRequest(recordedRequest);
+        assertThat(
+                body,
+                hasEntry(
+                        "grant_type",
+                        "urn:auth0:params:oauth:grant-type:token-exchange:federated-connection-access-token"));
+        assertThat(body, hasEntry("client_id", CLIENT_ID));
+        assertThat(body, hasEntry("client_secret", CLIENT_SECRET));
+        assertThat(body, hasEntry("subject_token", "test-refresh-token"));
+        assertThat(body, hasEntry("subject_token_type", "urn:ietf:params:oauth:token-type:refresh_token"));
+        assertThat(
+                body,
+                hasEntry(
+                        "requested_token_type", "http://auth0.com/oauth/token-type/federated-connection-access-token"));
+        assertThat(body, hasEntry("connection", "google-oauth2"));
+        assertThat(body, not(hasKey("login_hint")));
+
+        assertThat(response, is(notNullValue()));
+        assertThat(response.getAccessToken(), not(emptyOrNullString()));
+    }
+
+    @Test
+    public void shouldCreateGetTokenForConnectionRequestWithLoginHint() throws Exception {
+        TokenRequest request = api.getTokenForConnection("google-oauth2", "test-refresh-token", "google-user-id");
+        assertThat(request, is(notNullValue()));
+
+        server.jsonResponse(AUTH_TOKENS, 200);
+        TokenHolder response = request.execute().getBody();
+        RecordedRequest recordedRequest = server.takeRequest();
+
+        Map<String, Object> body = bodyFromRequest(recordedRequest);
+        assertThat(body, hasEntry("connection", "google-oauth2"));
+        assertThat(body, hasEntry("login_hint", "google-user-id"));
+
+        assertThat(response, is(notNullValue()));
+        assertThat(response.getAccessToken(), not(emptyOrNullString()));
+    }
+
+    @Test
+    public void getTokenForConnectionRequiresClientAuthentication() {
+        verifyThrows(
+                IllegalStateException.class,
+                () -> apiNoClientAuthentication.getTokenForConnection("google-oauth2", "test-refresh-token", null),
+                "A client secret or client assertion signing key is required for this operation");
+    }
+
     // Login with Passwordless
 
     @Test