question: public List < Challenge > challenges ( ) { String responseField ; if ( code == HTTP_UNAUTHORIZED ) { responseField = "WWW-Authenticate" ; } else if ( code == HTTP_PROXY_AUTH ) { responseField = "Proxy-Authenticate" ; } else { return Collections . emptyList ( ) ; } return OkHeaders . parseChallenges ( headers ( ) , responseField ) ; }
target:  Returns the authorization challenges appropriate for this response's code. If the response code is 401 unauthorized, this returns the "WWW-Authenticate" challenges. If the response code is 407 proxy unauthorized, this returns the "Proxy-Authenticate" challenges. Otherwise this returns an empty list of challenges.