*/
protected Response startAuthorization(MultivaluedMap<String, String> params) {
// Make sure the end user has authenticated, check if HTTPS is used
SecurityContext sc = getAndValidateSecurityContext();
Client client = getClient(params);
// Validate the provided request URI, if any, against the ones Client provided
// during the registration
String redirectUri = validateRedirectUri(client, params.getFirst(OAuthConstants.REDIRECT_URI));