Using Cognito to authorize users

Setup Cognito in serverless

Firstly, you have to add Cognito User Pool and User Pool Client resources to the serverless file:

    CognitoUserPool:
      Type: AWS::Cognito::UserPool
      Properties:
        UserPoolName: ${self:custom.CognitoUserPoolName}
        Policies:
          PasswordPolicy:
            RequireLowercase: true
            RequireSymbols: false
            RequireUppercase: false
            MinimumLength: 6
    CognitoUserPoolClient:
      Type: AWS::Cognito::UserPoolClient
      Properties:
        ClientName: user-pool-client
        UserPoolId:
          Ref: CognitoUserPool
        ExplicitAuthFlows:
          - ADMIN_NO_SRP_AUTH
        GenerateSecret: false

For convenience, we will declare a custom variable at the top level of the serverless file:

custom:
  CognitoUserPoolName: user-pool # Name for your cognito user pool

If you want to autoconfirm users who sign up, you need to add preSignUp function to your lambda functions list:

  preSignUp:
    handler: handler.preSignUp
    events:
      - cognitoUserPool:
          pool: ${self:custom.CognitoUserPoolName}
          trigger: PreSignUp
          existing: true

And write the following handler for this function

module.exports.preSignUp = async (event, context, callback) => {
  // Confirm the user
  event.response.autoConfirmUser = true;
  // Return to Amazon Cognito
  callback(null, event);
};

If you want to authorize your lambda functions using Cognito user pool, you need to add a resource Authorizer:

    MyCognitoAuthorizer:
      Type: AWS::ApiGateway::Authorizer
      Properties:
        AuthorizerResultTtlInSeconds: 300
        IdentitySource: method.request.header.Authorization
        RestApiId:
          Ref: ApiGatewayRestApi
        Name: MyCognitoAuthorizer
        Type: COGNITO_USER_POOLS
        ProviderARNs:
          - {"Fn::Join": ["", ["arn:aws:cognito-idp:", {Ref: "AWS::Region"}, ":", {Ref: "AWS::AccountId"}, ":userpool/", Ref: CognitoUserPool]]}

And add authorizer for selected function, for example:

functions:
  # This function will add note
  addNote:
    handler: handler.addNote
    events:
      - http:
          path: /add/
          method: put
          cors:
            origin: '*'
            headers: 
              - Content-Type
              - Authorization
            allowCredentials: false
          authorizer:
            type: COGNITO_USER_POOLS
            authorizerId:
              Ref: MyCognitoAuthorizer

Integrating frontend with Cognito using amazon-cognito-identity-js

Registering a user with the application. One needs to create a CognitoUserPool object by providing a UserPoolId and a ClientId and signing up by using a username, password.

var poolData = {
	UserPoolId: '...', // Your user pool id here
	ClientId: '...', // Your client id here
};
var userPool = new AmazonCognitoIdentity.CognitoUserPool(poolData);
userPool.signUp('username', 'password', attributeList, null, function(
	err,
	result
) {
	if (err) {
		alert(err.message || JSON.stringify(err));
		return;
	}
	var cognitoUser = result.user;
	console.log('user name is ' + cognitoUser.getUsername());
});

To login you need to authenticate a user with the Amazon Cognito Identity service.

var authenticationData = {
	Username: 'username',
	Password: 'password',
};
var authenticationDetails = new AmazonCognitoIdentity.AuthenticationDetails(
	authenticationData
);
var poolData = {
	UserPoolId: '...', // Your user pool id here
	ClientId: '...', // Your client id here
};
var userPool = new AmazonCognitoIdentity.CognitoUserPool(poolData);
var userData = {
	Username: 'username',
	Pool: userPool,
};
var cognitoUser = new AmazonCognitoIdentity.CognitoUser(userData);
cognitoUser.authenticateUser(authenticationDetails, {
	onSuccess: function(result) {
		var accessToken = result.getAccessToken().getJwtToken();
	},
	onFailure: function(err) {
		alert(err.message || JSON.stringify(err));
	},
});

Signing out from the application.

cognitoUser.signOut();

Retrieving the current user from local storage.

var poolData = {
	UserPoolId: '...', // Your user pool id here
	ClientId: '...', // Your client id here
};
var userPool = new AmazonCognitoIdentity.CognitoUserPool(poolData);
var cognitoUser = userPool.getCurrentUser();
if (cognitoUser != null) {
	cognitoUser.getSession(function(err, session) {
		if (err) {
			alert(err.message || JSON.stringify(err));
			return;
		}
		console.log('session validity: ' + session.isValid());
		// NOTE: getSession must be called to authenticate user before calling getUserAttributes
		cognitoUser.getUserAttributes(function(err, attributes) {
			if (err) {
				// Handle error
			} else {
				// Do something with attributes
			}
		});
	});
}

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