Trouble with callback and default parameter

[eluser]solid9[/eluser]
Actually your codes are confusing.
Not tested but try this,

Code:

function _validate_credentials($only_identity=FALSE){
     if($only_identity == FALSE){
      echo 'the param is FALSE!!';
      #...
     }
}

or you can try isset() also
Not tested but try,

Code:

function _validate_credentials($only_identity){
     if(!isset($only_identity)){
      echo 'the param is not SET!!';
      #...
     }
}