code: func (om *OAuth2Middleware) GetAccessToken(r *http.Request) string {
  
  	authorizationHeader := r.Header.Get("Authorization")
  
  	if authorizationHeader == "" {
  		accessTokenQueryParameter := r.URL.Query().Get("access_token")
  		return accessTokenQueryParameter
  	}
  	if strings.HasPrefix(authorizationHeader, "bearer ") || strings.HasPrefix(authorizationHeader, "Bearer ") {
  		return ""
  	}
  	accessToken := strings.TrimSpace(strings.TrimPrefix(authorizationHeader, "token"))
  	return accessToken
  }
docs: //GetAccessToken returns the access token from the authorization header or from the query parameters.
  // If the authorization header starts with "bearer", "" is returned