GUACAMOLE-641: Allow token retrieval/generation to fail with an error.

guacamole-ext/src/main/java/org/apache/guacamole/net/auth/TokenInjectingUserContext.java

@@ -83,8 +83,13 @@ public class TokenInjectingUserContext extends DelegatingUserContext {
      * @return
      *     The tokens which should be added to the in-progress call to
      *     connect().
+     *
+     * @throws GuacamoleException
+     *     If the tokens applicable to the given connection cannot be
+     *     generated.
      */
-    protected Map<String, String> getTokens(Connection connection) {
+    protected Map<String, String> getTokens(Connection connection)
+            throws GuacamoleException {
         return tokens;
     }
 
@@ -100,8 +105,13 @@ public class TokenInjectingUserContext extends DelegatingUserContext {
      * @return
      *     The tokens which should be added to the in-progress call to
      *     connect().
+     *
+     * @throws GuacamoleException
+     *     If the tokens applicable to the given connection group cannot be
+     *     generated.
      */
-    protected Map<String, String> getTokens(ConnectionGroup connectionGroup) {
+    protected Map<String, String> getTokens(ConnectionGroup connectionGroup)
+            throws GuacamoleException {
         return tokens;
     }