Rule Definition
Using LAContext evaluatePolicy: method provides a callback reply block reply:(void (^)(BOOL success, NSError *error))reply. The success returned value must be checked properly to avoid any misuse of the authentication check.

Remediation
Make sure you have implemented the check of success variable in the reply block callback

Violation Code Sample

let context = LAContext()
var authError: NSError?

var myLocalizedReasonString = "String explaining why app needs authentication"

if myContext.canEvaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, error:&authError) {
    myContext.evaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, localizedReason: myReasonString, reply: { (success: Bool, evalPolicyError: NSError?) -> Void in

       println("the user seems to be connected")

    })
} else{
    // Could not evaluate policy; check authError
}

Fixed Code Sample

let context = LAContext()
var authError: NSError?

var myLocalizedReasonString = "String explaining why app needs authentication"

if myContext.canEvaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, error:&authError) {
    myContext.evaluatePolicy(LAPolicy.DeviceOwnerAuthenticationWithBiometrics, localizedReason: myReasonString, reply: { (success: Bool, evalPolicyError: NSError?) -> Void in

        if success {
            // User authenticated successfully
        } else {
            // Authenticate failed
        }
    })
} else{
    // Could not evaluate policy; check authError
}

https://developer.apple.com/library/ios/documentation/LocalAuthentication/Reference/LocalAuthentication_Framework/