ios - Touch ID authentication without alert -

the following code show alert while authenticating. want authentication should happen in background, when unlock iphone's passcode lock using touch id.

  func touchidcheck(){             let authcontext:lacontext=lacontext()             var error:nserror?          if   authcontext.canevaluatepolicy(lapolicy.deviceownerauthenticationwithbiometrics, error: &error){             authcontext.evaluatepolicy(lapolicy.deviceownerauthenticationwithbiometrics, localizedreason: "testing", reply: {                 (wassuccessful:bool, error:nserror?) in                 if wassuccessful{                     print("yes")}                  else                 {                     print("no")                 }                 }             )         }          }