code: func (m *OAuth2Method) GetUserCredentials(c context.Context, r *http.Request) (*oauth2.Token, error) {
  	chunks := strings.SplitN(r.Header.Get("Authorization"), " ", 2)
  	if len(chunks) != 2 || (chunks[0] != "OAuth" && chunks[0] != "Bearer") {
  		return nil, errBadAuthHeader
  	}
  	return &oauth2.Token{
  		AccessToken: chunks[1],
  		TokenType:   "Bearer",
  	}, nil
  }
docs: // GetUserCredentials implements auth.UserCredentialsGetter.