An exception raised when OAuth2 authorization fails.

class AuthorizationException implements Exception {
 /// The name of the error. Possible names are enumerated in [the spec][].
 ///
 /// [the spec]: http://tools.ietf.org/html/draft-ietf-oauth-v2-31#section-5.2
 final String error;

 /// The description of the error, provided by the server. Defaults to null.
 final String description;

 /// A URI for a page that describes the error in more detail, provided by the
 /// server. Defaults to null.
 final Uri uri;

 /// Creates an AuthorizationException.
 AuthorizationException(this.error, this.description, this.uri);

 /// Provides a string description of the AuthorizationException.
 String toString() {
   var header = 'OAuth authorization error ($error)';
   if (description != null) {
     header = '$header: $description';
   } else if (uri != null) {
     header = '$header: $uri';
   }
   return '$header.';
 }
}