AWS Cognito User Pools with mobile sdk for iOS using custom challenge
I was integrating AWS Cognito user pool to an iOS application. The sign in feature is using custom challenge for authentication, but there is a lack of documentation about how to use the iOS sdk. After many trial and errors, I have finally able to sign in success, so I’m going to document the steps as shown below:
Step 1: Create a CognitoUserPool
In AppDelegate, after didFinishLaunchingWithOptions, the user pool is initialised.
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
// setup service configuration
let serviceConfiguration = AWSServiceConfiguration(region: CognitoIdentityUserPoolRegion, credentialsProvider: nil
// create pool configuration
let poolConfiguration = AWSCognitoIdentityUserPoolConfiguration(clientId: CognitoIdentityUserPoolAppClientId, clientSecret: nil, poolId: CognitoIdentityUserPoolId)
// initialize user pool client
AWSCognitoIdentityUserPool.register(with: serviceConfiguration, userPoolConfiguration: poolConfiguration, forKey: AWSCognitoUserPoolsSignInProviderKey)
// fetch the user pool client we initialized in above step
let pool = AWSCognitoIdentityUserPool(forKey: AWSCognitoUserPoolsSignInProviderKey)
self.storyboard = UIStoryboard(name: “Main”, bundle: nil)
pool.delegate = self
return true
}
Step 2: Implement the protocol delegate
extension AppDelegate: AWSCognitoIdentityCustomAuthentication{
func didCompleteStepWithError(_ error: Error?) {
}
func getCustomChallengeDetails(_ authenticationInput: AWSCognitoIdentityCustomAuthenticationInput, customAuthCompletionSource: AWSTaskCompletionSource<AWSCognitoIdentityCustomChallengeDetails>) {
}
func startCustomAuthentication() -> AWSCognitoIdentityCustomAuthentication {
if (self.navigationController == nil) {
self.navigationController = self.storyboard?.instantiateViewController(withIdentifier: “signinController”) as? UINavigationController
}
if (self.signInViewController == nil) {
self.signInViewController = self.navigationController?.viewControllers[0] as? SignInViewController
}
DispatchQueue.main.async {
self.navigationController!.popToRootViewController(animated: true)
if (!self.navigationController!.isViewLoaded
|| self.navigationController!.view.window == nil) {
self.window?.rootViewController?.present(self.navigationController!,
animated: true,
completion: nil)
}
}
return self.signInViewController!
}
}
Step 3: Handle the custom challenge inside the sign in view controller
extension SignInViewController: AWSCognitoIdentityCustomAuthentication {
func getCustomChallengeDetails(_ authenticationInput: AWSCognitoIdentityCustomAuthenticationInput, customAuthCompletionSource: AWSTaskCompletionSource<AWSCognitoIdentityCustomChallengeDetails>) {
let authDetails = AWSCognitoIdentityCustomChallengeDetails(challengeResponses: [“USERNAME”:”YourUserName”, “ANSWER”: “123456”])
customAuthCompletionSource.set(result: authDetails)
}
public func didCompleteStepWithError(_ error: Error?) {
DispatchQueue.main.async {
if let error = error as? NSError {
print(“error”)
} else {
print(“success”)
self.dismiss(animated: true, completion: nil)
}
}
}
}
Step 4: After sign in success, you can get the username and user attribute:
self.user?.getDetails().continueOnSuccessWith { (task) -> AnyObject? in
DispatchQueue.main.async(execute: {
self.response = task.result
// With user details
print(response)
})
return nil
}
Please let me know if you have any questions. I hope AWS could update the documentations and provide sample example code to save us time to understand the sdk through trial and error.

About
Experience in software development, application architecture, and deploying cloud solutions for enterprise customers. Strong hands-on skills with a Master's degree in Computer Science and business acumen with a master of business administration (MBA) in Finance. Certified in Amazon Web Services (AWS), Google Cloud Platform (GCP), Microsoft Azure, Kubernetes (CKA, CKAD, CKS, KCNA) and Scrum (PSM, PSPO) with experience in building banking products from scratch.