Automatically confirm known Amazon Cognito users with a Lambda function using an Amazon SDK - Amazon Lambda
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Automatically confirm known Amazon Cognito users with a Lambda function using an Amazon SDK

The following code example shows how to automatically confirm known Amazon Cognito users with a Lambda function.

  • Configure a user pool to call a Lambda function for the PreSignUp trigger.

  • Sign up a user with Amazon Cognito.

  • The Lambda function scans a DynamoDB table and automatically confirms known users.

  • Sign in as the new user, then clean up resources.

SDK for Go V2

There's more on GitHub. Find the complete example and learn how to set up and run in the Amazon Code Examples Repository.

Run an interactive scenario at a command prompt.

// AutoConfirm separates the steps of this scenario into individual functions so that // they are simpler to read and understand. type AutoConfirm struct { helper IScenarioHelper questioner demotools.IQuestioner resources Resources cognitoActor *actions.CognitoActions } // NewAutoConfirm constructs a new auto confirm runner. func NewAutoConfirm(sdkConfig aws.Config, questioner demotools.IQuestioner, helper IScenarioHelper) AutoConfirm { scenario := AutoConfirm{ helper: helper, questioner: questioner, resources: Resources{}, cognitoActor: &actions.CognitoActions{CognitoClient: cognitoidentityprovider.NewFromConfig(sdkConfig)}, } scenario.resources.init(scenario.cognitoActor, questioner) return scenario } // AddPreSignUpTrigger adds a Lambda handler as an invocation target for the PreSignUp trigger. func (runner *AutoConfirm) AddPreSignUpTrigger(userPoolId string, functionArn string) { log.Printf("Let's add a Lambda function to handle the PreSignUp trigger from Cognito.\n" + "This trigger happens when a user signs up, and lets your function take action before the main Cognito\n" + "sign up processing occurs.\n") err := runner.cognitoActor.UpdateTriggers( userPoolId, actions.TriggerInfo{Trigger: actions.PreSignUp, HandlerArn: aws.String(functionArn)}) if err != nil { panic(err) } log.Printf("Lambda function %v added to user pool %v to handle the PreSignUp trigger.\n", functionArn, userPoolId) } // SignUpUser signs up a user from the known user table with a password you specify. func (runner *AutoConfirm) SignUpUser(clientId string, usersTable string) (string, string) { log.Println("Let's sign up a user to your Cognito user pool. When the user's email matches an email in the\n" + "DynamoDB known users table, it is automatically verified and the user is confirmed.") knownUsers, err := runner.helper.GetKnownUsers(usersTable) if err != nil { panic(err) } userChoice := runner.questioner.AskChoice("Which user do you want to use?\n", knownUsers.UserNameList()) user := knownUsers.Users[userChoice] var signedUp bool var userConfirmed bool password := runner.questioner.AskPassword("Enter a password that has at least eight characters, uppercase, lowercase, numbers and symbols.\n"+ "(the password will not display as you type):", 8) for !signedUp { log.Printf("Signing up user '%v' with email '%v' to Cognito.\n", user.UserName, user.UserEmail) userConfirmed, err = runner.cognitoActor.SignUp(clientId, user.UserName, password, user.UserEmail) if err != nil { var invalidPassword *types.InvalidPasswordException if errors.As(err, &invalidPassword) { password = runner.questioner.AskPassword("Enter another password:", 8) } else { panic(err) } } else { signedUp = true } } log.Printf("User %v signed up, confirmed = %v.\n", user.UserName, userConfirmed) log.Println(strings.Repeat("-", 88)) return user.UserName, password } // SignInUser signs in a user. func (runner *AutoConfirm) SignInUser(clientId string, userName string, password string) string { runner.questioner.Ask("Press Enter when you're ready to continue.") log.Printf("Let's sign in as %v...\n", userName) authResult, err := runner.cognitoActor.SignIn(clientId, userName, password) if err != nil { panic(err) } log.Printf("Successfully signed in. Your access token starts with: %v...\n", (*authResult.AccessToken)[:10]) log.Println(strings.Repeat("-", 88)) return *authResult.AccessToken } // Run runs the scenario. func (runner *AutoConfirm) Run(stackName string) { defer func() { if r := recover(); r != nil { log.Println("Something went wrong with the demo.") runner.resources.Cleanup() } }() log.Println(strings.Repeat("-", 88)) log.Printf("Welcome\n") log.Println(strings.Repeat("-", 88)) stackOutputs, err := runner.helper.GetStackOutputs(stackName) if err != nil { panic(err) } runner.resources.userPoolId = stackOutputs["UserPoolId"] runner.helper.PopulateUserTable(stackOutputs["TableName"]) runner.AddPreSignUpTrigger(stackOutputs["UserPoolId"], stackOutputs["AutoConfirmFunctionArn"]) runner.resources.triggers = append(runner.resources.triggers, actions.PreSignUp) userName, password := runner.SignUpUser(stackOutputs["UserPoolClientId"], stackOutputs["TableName"]) runner.helper.ListRecentLogEvents(stackOutputs["AutoConfirmFunction"]) runner.resources.userAccessTokens = append(runner.resources.userAccessTokens, runner.SignInUser(stackOutputs["UserPoolClientId"], userName, password)) runner.resources.Cleanup() log.Println(strings.Repeat("-", 88)) log.Println("Thanks for watching!") log.Println(strings.Repeat("-", 88)) }

Handle the PreSignUp trigger with a Lambda function.

const TABLE_NAME = "TABLE_NAME" // UserInfo defines structured user data that can be marshalled to a DynamoDB format. type UserInfo struct { UserName string `dynamodbav:"UserName"` UserEmail string `dynamodbav:"UserEmail"` } // GetKey marshals the user email value to a DynamoDB key format. func (user UserInfo) GetKey() map[string]dynamodbtypes.AttributeValue { userEmail, err := attributevalue.Marshal(user.UserEmail) if err != nil { panic(err) } return map[string]dynamodbtypes.AttributeValue{"UserEmail": userEmail} } type handler struct { dynamoClient *dynamodb.Client } // HandleRequest handles the PreSignUp event by looking up a user in an Amazon DynamoDB table and // specifying whether they should be confirmed and verified. func (h *handler) HandleRequest(ctx context.Context, event events.CognitoEventUserPoolsPreSignup) (events.CognitoEventUserPoolsPreSignup, error) { log.Printf("Received presignup from %v for user '%v'", event.TriggerSource, event.UserName) if event.TriggerSource != "PreSignUp_SignUp" { // Other trigger sources, such as PreSignUp_AdminInitiateAuth, ignore the response from this handler. return event, nil } tableName := os.Getenv(TABLE_NAME) user := UserInfo{ UserEmail: event.Request.UserAttributes["email"], } log.Printf("Looking up email %v in table %v.\n", user.UserEmail, tableName) output, err := h.dynamoClient.GetItem(ctx, &dynamodb.GetItemInput{ Key: user.GetKey(), TableName: aws.String(tableName), }) if err != nil { log.Printf("Error looking up email %v.\n", user.UserEmail) return event, err } if output.Item == nil { log.Printf("Email %v not found. Email verification is required.\n", user.UserEmail) return event, err } err = attributevalue.UnmarshalMap(output.Item, &user) if err != nil { log.Printf("Couldn't unmarshal DynamoDB item. Here's why: %v\n", err) return event, err } if user.UserName != event.UserName { log.Printf("UserEmail %v found, but stored UserName '%v' does not match supplied UserName '%v'. Verification is required.\n", user.UserEmail, user.UserName, event.UserName) } else { log.Printf("UserEmail %v found with matching UserName %v. User is confirmed.\n", user.UserEmail, user.UserName) event.Response.AutoConfirmUser = true event.Response.AutoVerifyEmail = true } return event, err } func main() { sdkConfig, err := config.LoadDefaultConfig(context.TODO()) if err != nil { log.Panicln(err) } h := handler{ dynamoClient: dynamodb.NewFromConfig(sdkConfig), } lambda.Start(h.HandleRequest) }

Create a struct that performs common tasks.

// IScenarioHelper defines common functions used by the workflows in this example. type IScenarioHelper interface { Pause(secs int) GetStackOutputs(stackName string) (actions.StackOutputs, error) PopulateUserTable(tableName string) GetKnownUsers(tableName string) (actions.UserList, error) AddKnownUser(tableName string, user actions.User) ListRecentLogEvents(functionName string) } // ScenarioHelper contains AWS wrapper structs used by the workflows in this example. type ScenarioHelper struct { questioner demotools.IQuestioner dynamoActor *actions.DynamoActions cfnActor *actions.CloudFormationActions cwlActor *actions.CloudWatchLogsActions isTestRun bool } // NewScenarioHelper constructs a new scenario helper. func NewScenarioHelper(sdkConfig aws.Config, questioner demotools.IQuestioner) ScenarioHelper { scenario := ScenarioHelper{ questioner: questioner, dynamoActor: &actions.DynamoActions{DynamoClient: dynamodb.NewFromConfig(sdkConfig)}, cfnActor: &actions.CloudFormationActions{CfnClient: cloudformation.NewFromConfig(sdkConfig)}, cwlActor: &actions.CloudWatchLogsActions{CwlClient: cloudwatchlogs.NewFromConfig(sdkConfig)}, } return scenario } // Pause waits for the specified number of seconds. func (helper ScenarioHelper) Pause(secs int) { if !helper.isTestRun { time.Sleep(time.Duration(secs) * time.Second) } } // GetStackOutputs gets the outputs from the specified CloudFormation stack in a structured format. func (helper ScenarioHelper) GetStackOutputs(stackName string) (actions.StackOutputs, error) { return helper.cfnActor.GetOutputs(stackName), nil } // PopulateUserTable fills the known user table with example data. func (helper ScenarioHelper) PopulateUserTable(tableName string) { log.Printf("First, let's add some users to the DynamoDB %v table we'll use for this example.\n", tableName) err := helper.dynamoActor.PopulateTable(tableName) if err != nil { panic(err) } } // GetKnownUsers gets the users from the known users table in a structured format. func (helper ScenarioHelper) GetKnownUsers(tableName string) (actions.UserList, error) { knownUsers, err := helper.dynamoActor.Scan(tableName) if err != nil { log.Printf("Couldn't get known users from table %v. Here's why: %v\n", tableName, err) } return knownUsers, err } // AddKnownUser adds a user to the known users table. func (helper ScenarioHelper) AddKnownUser(tableName string, user actions.User) { log.Printf("Adding user '%v' with email '%v' to the DynamoDB known users table...\n", user.UserName, user.UserEmail) err := helper.dynamoActor.AddUser(tableName, user) if err != nil { panic(err) } } // ListRecentLogEvents gets the most recent log stream and events for the specified Lambda function and displays them. func (helper ScenarioHelper) ListRecentLogEvents(functionName string) { log.Println("Waiting a few seconds to let Lambda write to CloudWatch Logs...") helper.Pause(10) log.Println("Okay, let's check the logs to find what's happened recently with your Lambda function.") logStream, err := helper.cwlActor.GetLatestLogStream(functionName) if err != nil { panic(err) } log.Printf("Getting some recent events from log stream %v\n", *logStream.LogStreamName) events, err := helper.cwlActor.GetLogEvents(functionName, *logStream.LogStreamName, 10) if err != nil { panic(err) } for _, event := range events { log.Printf("\t%v", *event.Message) } log.Println(strings.Repeat("-", 88)) }

Create a struct that wraps Amazon Cognito actions.

type CognitoActions struct { CognitoClient *cognitoidentityprovider.Client } // Trigger and TriggerInfo define typed data for updating an Amazon Cognito trigger. type Trigger int const ( PreSignUp Trigger = iota UserMigration PostAuthentication ) type TriggerInfo struct { Trigger Trigger HandlerArn *string } // UpdateTriggers adds or removes Lambda triggers for a user pool. When a trigger is specified with a `nil` value, // it is removed from the user pool. func (actor CognitoActions) UpdateTriggers(userPoolId string, triggers ...TriggerInfo) error { output, err := actor.CognitoClient.DescribeUserPool(context.TODO(), &cognitoidentityprovider.DescribeUserPoolInput{ UserPoolId: aws.String(userPoolId), }) if err != nil { log.Printf("Couldn't get info about user pool %v. Here's why: %v\n", userPoolId, err) return err } lambdaConfig := output.UserPool.LambdaConfig for _, trigger := range triggers { switch trigger.Trigger { case PreSignUp: lambdaConfig.PreSignUp = trigger.HandlerArn case UserMigration: lambdaConfig.UserMigration = trigger.HandlerArn case PostAuthentication: lambdaConfig.PostAuthentication = trigger.HandlerArn } } _, err = actor.CognitoClient.UpdateUserPool(context.TODO(), &cognitoidentityprovider.UpdateUserPoolInput{ UserPoolId: aws.String(userPoolId), LambdaConfig: lambdaConfig, }) if err != nil { log.Printf("Couldn't update user pool %v. Here's why: %v\n", userPoolId, err) } return err } // SignUp signs up a user with Amazon Cognito. func (actor CognitoActions) SignUp(clientId string, userName string, password string, userEmail string) (bool, error) { confirmed := false output, err := actor.CognitoClient.SignUp(context.TODO(), &cognitoidentityprovider.SignUpInput{ ClientId: aws.String(clientId), Password: aws.String(password), Username: aws.String(userName), UserAttributes: []types.AttributeType{ {Name: aws.String("email"), Value: aws.String(userEmail)}, }, }) if err != nil { var invalidPassword *types.InvalidPasswordException if errors.As(err, &invalidPassword) { log.Println(*invalidPassword.Message) } else { log.Printf("Couldn't sign up user %v. Here's why: %v\n", userName, err) } } else { confirmed = output.UserConfirmed } return confirmed, err } // SignIn signs in a user to Amazon Cognito using a username and password authentication flow. func (actor CognitoActions) SignIn(clientId string, userName string, password string) (*types.AuthenticationResultType, error) { var authResult *types.AuthenticationResultType output, err := actor.CognitoClient.InitiateAuth(context.TODO(), &cognitoidentityprovider.InitiateAuthInput{ AuthFlow: "USER_PASSWORD_AUTH", ClientId: aws.String(clientId), AuthParameters: map[string]string{"USERNAME": userName, "PASSWORD": password}, }) if err != nil { var resetRequired *types.PasswordResetRequiredException if errors.As(err, &resetRequired) { log.Println(*resetRequired.Message) } else { log.Printf("Couldn't sign in user %v. Here's why: %v\n", userName, err) } } else { authResult = output.AuthenticationResult } return authResult, err } // ForgotPassword starts a password recovery flow for a user. This flow typically sends a confirmation code // to the user's configured notification destination, such as email. func (actor CognitoActions) ForgotPassword(clientId string, userName string) (*types.CodeDeliveryDetailsType, error) { output, err := actor.CognitoClient.ForgotPassword(context.TODO(), &cognitoidentityprovider.ForgotPasswordInput{ ClientId: aws.String(clientId), Username: aws.String(userName), }) if err != nil { log.Printf("Couldn't start password reset for user '%v'. Here;s why: %v\n", userName, err) } return output.CodeDeliveryDetails, err } // ConfirmForgotPassword confirms a user with a confirmation code and a new password. func (actor CognitoActions) ConfirmForgotPassword(clientId string, code string, userName string, password string) error { _, err := actor.CognitoClient.ConfirmForgotPassword(context.TODO(), &cognitoidentityprovider.ConfirmForgotPasswordInput{ ClientId: aws.String(clientId), ConfirmationCode: aws.String(code), Password: aws.String(password), Username: aws.String(userName), }) if err != nil { var invalidPassword *types.InvalidPasswordException if errors.As(err, &invalidPassword) { log.Println(*invalidPassword.Message) } else { log.Printf("Couldn't confirm user %v. Here's why: %v", userName, err) } } return err } // DeleteUser removes a user from the user pool. func (actor CognitoActions) DeleteUser(userAccessToken string) error { _, err := actor.CognitoClient.DeleteUser(context.TODO(), &cognitoidentityprovider.DeleteUserInput{ AccessToken: aws.String(userAccessToken), }) if err != nil { log.Printf("Couldn't delete user. Here's why: %v\n", err) } return err } // AdminCreateUser uses administrator credentials to add a user to a user pool. This method leaves the user // in a state that requires they enter a new password next time they sign in. func (actor CognitoActions) AdminCreateUser(userPoolId string, userName string, userEmail string) error { _, err := actor.CognitoClient.AdminCreateUser(context.TODO(), &cognitoidentityprovider.AdminCreateUserInput{ UserPoolId: aws.String(userPoolId), Username: aws.String(userName), MessageAction: types.MessageActionTypeSuppress, UserAttributes: []types.AttributeType{{Name: aws.String("email"), Value: aws.String(userEmail)}}, }) if err != nil { var userExists *types.UsernameExistsException if errors.As(err, &userExists) { log.Printf("User %v already exists in the user pool.", userName) err = nil } else { log.Printf("Couldn't create user %v. Here's why: %v\n", userName, err) } } return err } // AdminSetUserPassword uses administrator credentials to set a password for a user without requiring a // temporary password. func (actor CognitoActions) AdminSetUserPassword(userPoolId string, userName string, password string) error { _, err := actor.CognitoClient.AdminSetUserPassword(context.TODO(), &cognitoidentityprovider.AdminSetUserPasswordInput{ Password: aws.String(password), UserPoolId: aws.String(userPoolId), Username: aws.String(userName), Permanent: true, }) if err != nil { var invalidPassword *types.InvalidPasswordException if errors.As(err, &invalidPassword) { log.Println(*invalidPassword.Message) } else { log.Printf("Couldn't set password for user %v. Here's why: %v\n", userName, err) } } return err }

Create a struct that wraps DynamoDB actions.

// DynamoActions encapsulates the Amazon Simple Notification Service (Amazon SNS) actions // used in the examples. type DynamoActions struct { DynamoClient *dynamodb.Client } // User defines structured user data. type User struct { UserName string UserEmail string LastLogin *LoginInfo `dynamodbav:",omitempty"` } // LoginInfo defines structured custom login data. type LoginInfo struct { UserPoolId string ClientId string Time string } // UserList defines a list of users. type UserList struct { Users []User } // UserNameList returns the usernames contained in a UserList as a list of strings. func (users *UserList) UserNameList() []string { names := make([]string, len(users.Users)) for i := 0; i < len(users.Users); i++ { names[i] = users.Users[i].UserName } return names } // PopulateTable adds a set of test users to the table. func (actor DynamoActions) PopulateTable(tableName string) error { var err error var item map[string]types.AttributeValue var writeReqs []types.WriteRequest for i := 1; i < 4; i++ { item, err = attributevalue.MarshalMap(User{UserName: fmt.Sprintf("test_user_%v", i), UserEmail: fmt.Sprintf("", i)}) if err != nil { log.Printf("Couldn't marshall user into DynamoDB format. Here's why: %v\n", err) return err } writeReqs = append(writeReqs, types.WriteRequest{PutRequest: &types.PutRequest{Item: item}}) } _, err = actor.DynamoClient.BatchWriteItem(context.TODO(), &dynamodb.BatchWriteItemInput{ RequestItems: map[string][]types.WriteRequest{tableName: writeReqs}, }) if err != nil { log.Printf("Couldn't populate table %v with users. Here's why: %v\n", tableName, err) } return err } // Scan scans the table for all items. func (actor DynamoActions) Scan(tableName string) (UserList, error) { var userList UserList output, err := actor.DynamoClient.Scan(context.TODO(), &dynamodb.ScanInput{ TableName: aws.String(tableName), }) if err != nil { log.Printf("Couldn't scan table %v for items. Here's why: %v\n", tableName, err) } else { err = attributevalue.UnmarshalListOfMaps(output.Items, &userList.Users) if err != nil { log.Printf("Couldn't unmarshal items into users. Here's why: %v\n", err) } } return userList, err } // AddUser adds a user item to a table. func (actor DynamoActions) AddUser(tableName string, user User) error { userItem, err := attributevalue.MarshalMap(user) if err != nil { log.Printf("Couldn't marshall user to item. Here's why: %v\n", err) } _, err = actor.DynamoClient.PutItem(context.TODO(), &dynamodb.PutItemInput{ Item: userItem, TableName: aws.String(tableName), }) if err != nil { log.Printf("Couldn't put item in table %v. Here's why: %v", tableName, err) } return err }

Create a struct that wraps CloudWatch Logs actions.

type CloudWatchLogsActions struct { CwlClient *cloudwatchlogs.Client } // GetLatestLogStream gets the most recent log stream for a Lambda function. func (actor CloudWatchLogsActions) GetLatestLogStream(functionName string) (types.LogStream, error) { var logStream types.LogStream logGroupName := fmt.Sprintf("/aws/lambda/%s", functionName) output, err := actor.CwlClient.DescribeLogStreams(context.TODO(), &cloudwatchlogs.DescribeLogStreamsInput{ Descending: aws.Bool(true), Limit: aws.Int32(1), LogGroupName: aws.String(logGroupName), OrderBy: types.OrderByLastEventTime, }) if err != nil { log.Printf("Couldn't get log streams for log group %v. Here's why: %v\n", logGroupName, err) } else { logStream = output.LogStreams[0] } return logStream, err } // GetLogEvents gets the most recent eventCount events from the specified log stream. func (actor CloudWatchLogsActions) GetLogEvents(functionName string, logStreamName string, eventCount int32) ( []types.OutputLogEvent, error) { var events []types.OutputLogEvent logGroupName := fmt.Sprintf("/aws/lambda/%s", functionName) output, err := actor.CwlClient.GetLogEvents(context.TODO(), &cloudwatchlogs.GetLogEventsInput{ LogStreamName: aws.String(logStreamName), Limit: aws.Int32(eventCount), LogGroupName: aws.String(logGroupName), }) if err != nil { log.Printf("Couldn't get log event for log stream %v. Here's why: %v\n", logStreamName, err) } else { events = output.Events } return events, err }

Create a struct that wraps Amazon CloudFormation actions.

// StackOutputs defines a map of outputs from a specific stack. type StackOutputs map[string]string type CloudFormationActions struct { CfnClient *cloudformation.Client } // GetOutputs gets the outputs from a CloudFormation stack and puts them into a structured format. func (actor CloudFormationActions) GetOutputs(stackName string) StackOutputs { output, err := actor.CfnClient.DescribeStacks(context.TODO(), &cloudformation.DescribeStacksInput{ StackName: aws.String(stackName), }) if err != nil || len(output.Stacks) == 0 { log.Panicf("Couldn't find a CloudFormation stack named %v. Here's why: %v\n", stackName, err) } stackOutputs := StackOutputs{} for _, out := range output.Stacks[0].Outputs { stackOutputs[*out.OutputKey] = *out.OutputValue } return stackOutputs }

Clean up resources.

// Resources keeps track of AWS resources created during an example and handles // cleanup when the example finishes. type Resources struct { userPoolId string userAccessTokens []string triggers []actions.Trigger cognitoActor *actions.CognitoActions questioner demotools.IQuestioner } func (resources *Resources) init(cognitoActor *actions.CognitoActions, questioner demotools.IQuestioner) { resources.userAccessTokens = []string{} resources.triggers = []actions.Trigger{} resources.cognitoActor = cognitoActor resources.questioner = questioner } // Cleanup deletes all AWS resources created during an example. func (resources *Resources) Cleanup() { defer func() { if r := recover(); r != nil { log.Printf("Something went wrong during cleanup.\n%v\n", r) log.Println("Use the AWS Management Console to remove any remaining resources \n" + "that were created for this scenario.") } }() wantDelete := resources.questioner.AskBool("Do you want to remove all of the AWS resources that were created "+ "during this demo (y/n)?", "y") if wantDelete { for _, accessToken := range resources.userAccessTokens { err := resources.cognitoActor.DeleteUser(accessToken) if err != nil { log.Println("Couldn't delete user during cleanup.") panic(err) } log.Println("Deleted user.") } triggerList := make([]actions.TriggerInfo, len(resources.triggers)) for i := 0; i < len(resources.triggers); i++ { triggerList[i] = actions.TriggerInfo{Trigger: resources.triggers[i], HandlerArn: nil} } err := resources.cognitoActor.UpdateTriggers(resources.userPoolId, triggerList...) if err != nil { log.Println("Couldn't update Cognito triggers during cleanup.") panic(err) } log.Println("Removed Cognito triggers from user pool.") } else { log.Println("Be sure to remove resources when you're done with them to avoid unexpected charges!") } }

For a complete list of Amazon SDK developer guides and code examples, see Using Lambda with an Amazon SDK. This topic also includes information about getting started and details about previous SDK versions.