getAuthorizationUrl method Null safety

Uri getAuthorizationUrl(
  1. Uri redirect,
  2. {Iterable<String>? scopes,
  3. String? state}

Returns the URL to which the resource owner should be redirected to authorize this client.

The resource owner will then be redirected to redirect, which should point to a server controlled by the client. This redirect will have additional query parameters that should be passed to handleAuthorizationResponse.

The specific permissions being requested from the authorization server may be specified via scopes. The scope strings are specific to the authorization server and may be found in its documentation. Note that you may not be granted access to every scope you request; you may check the Credentials.scopes field of Client.credentials to see which scopes you were granted.

An opaque state string may also be passed that will be present in the query parameters provided to the redirect URL.

It is a StateError to call this more than once.


Uri getAuthorizationUrl(Uri redirect,
    {Iterable<String>? scopes, String? state}) {
  if (_state != _State.initial) {
    throw StateError('The authorization URL has already been generated.');
  _state = _State.awaitingResponse;

  var scopeList = scopes?.toList() ?? <String>[];
  var codeChallenge = base64Url
      .replaceAll('=', '');

  _redirectEndpoint = redirect;
  _scopes = scopeList;
  _stateString = state;
  var parameters = {
    'response_type': 'code',
    'client_id': identifier,
    'redirect_uri': redirect.toString(),
    'code_challenge': codeChallenge,
    'code_challenge_method': 'S256'

  if (state != null) parameters['state'] = state;
  if (scopeList.isNotEmpty) parameters['scope'] = scopeList.join(_delimiter);

  return addQueryParameters(authorizationEndpoint, parameters);