Working with custom identity providers - AWS Transfer Family
Custom identity providersImplementing your API Gateway methodExample Lambda functions

Working with custom identity providers

To integrate your existing identity provider into AWS Transfer Family, provide a RESTful interface with a single Amazon API Gateway method. Transfer Family calls this method to authenticate your users.

This single method authenticates and authorizes your users for access to Amazon S3 or Amazon Elastic File System (Amazon EFS). After you configure the method, attach it to your server when you create a new server. You can create a new server using the AWS Transfer Family console or the CreateServer API operation.

For more information about working with Amazon API Gateway, see the API Gateway Developer Guide.

Authenticating using custom identity providers

To create a custom identity provider for Transfer Family, use API Gateway, which provides a highly secure way for you to create and provide APIs. With API Gateway, you can create an HTTPS endpoint so that all incoming API calls are transmitted with greater security. For more details about the API Gateway service, see the API Gateway Developer Guide.

API Gateway offers an authentication method named AWS_IAM, which gives you the same authentication based on AWS Identity and Access Management (IAM) that AWS uses internally. If you enable authentication with AWS_IAM, only callers with explicit permissions to call an API can reach that API's API Gateway method.

To use your API Gateway method as a custom identity provider for Transfer Family, enable IAM for your API Gateway method. As part of this process, you provide an IAM role with permissions for Transfer Family to use your gateway.

Note

To improve security, you can configure a web application firewall. AWS WAF is a web application firewall that lets you monitor the HTTP and HTTPS requests that are forwarded to an Amazon API Gateway. For details, see Add a web application firewall.

To use your API Gateway method for custom authentication with Transfer Family

  1. Create an AWS CloudFormation stack. To do this:

    1. Open the AWS CloudFormation console at https://console.aws.amazon.com/cloudformation.

    2. Follow the instructions on deploying an AWS CloudFormation stack from an existing template in Selecting a stack template in the AWS CloudFormation User Guide.

    3. Use one of the following basic templates to create an AWS Lambda-backed API Gateway method for use as a custom identity provider in Transfer Family.

    Deploying one of these stacks is the easiest way to integrate a custom identity provider into the Transfer Family workflow. Each stack uses the Lambda function to support your API method based on API Gateway. You can then use your API method as a custom identity provider in Transfer Family. By default, the Lambda function authenticates a single user called myuser with a password of MySuperSecretPassword. After deployment, you can edit these credentials or update the Lambda function code to do something different.

    Important

    We recommend that you edit the default user and password credentials.

    After the stack has been deployed, you can view details about it on the Outputs tab in the CloudFormation console. These details include the stack's Amazon Resource Name (ARN), the ARN of the IAM role that the stack created, and the URL for your new gateway.

    Note

    If you are using the custom identity provider option to enable password–based authentication for your users, and you enable the request and response logging provided by API Gateway, API Gateway will log your users' passwords to your Amazon CloudWatch Logs. We don't recommend using this log in your production environment. For more information, see Set up CloudWatch API logging in API Gateway in the API Gateway Developer Guide.

  2. Check the API Gateway method configuration for your server. To do this:

    1. Open the API Gateway console at https://console.aws.amazon.com/apigateway/.

    2. Choose the Transfer Custom Identity Provider basic template API that the AWS CloudFormation template generated.

      The following screenshot shows the complete API configuration. In this example, the method is backed by a Lambda function, but many other integration types are also possible.

    3. In the Resources pane, choose GET, and then choose Method Request. The following screenshot shows the correct method configuration.

    At this point, your API gateway is ready to be deployed.

  3. For Actions, choose Deploy API. For Deployment stage, choose prod, and then choose Deploy.

    After the API Gateway method is successfully deployed, view its performance in the Stage Editor section, as shown in the following screenshot.

    Note

    Copy the Invoke URL address that appears at the top of the screen. You will need it for the next step.

  4. Open the AWS Transfer Family console at https://console.aws.amazon.com/transfer/.

  5. Choose Create server to open the Create server page. For Choose an identity provider, choose Custom, as shown in the following screenshot.

    The invocation role contains the AWS CloudFormation stack name that you selected for the stack that you created in step 1. It has the following format: CloudFormation-stack-name-TransferIdentityProviderRole-ABC123DEF456GHI.

  6. For Custom provider, paste the Invoke URL address of the API Gateway endpoint that you created in the previous step.

  7. For Invocation role, choose the IAM role that was created by the AWS CloudFormation template. This role allows Transfer Family to invoke your API gateway method.

  8. Fill in the remaining boxes, and then choose Create server.

Testing your configuration

After you create your custom identity provider, you should test your configuration.

Console

To test your configuration by using the AWS Transfer Family console

  1. Open the AWS Transfer Family console at https://console.aws.amazon.com/transfer/.

  2. On the Servers page, choose your new server, choose Actions, and then choose Test.

  3. Enter the text for Username and Password that you set when you deployed the AWS CloudFormation stack. If you kept the default options, the user name is myuser and the password is MySuperSecretPassword.

  4. Choose the Server protocol and enter the IP address for Source IP, if you set them when you deployed the AWS CloudFormation stack.

    If user authentication succeeds, the test returns a StatusCode: 200 HTML response and a JSON object containing the details of the user's roles and permissions, as shown in the following screenshot.

CLI

To test your configuration by using the AWS CLI

  1. Run the test-identity-provider command. 

    aws transfer test-identity-provider --server-id s-1234abcd5678efgh --user-name myuser --user-password MySuperSecretPassword --server-protocol FTP --source-ip 127.0.0.1

  2. Enter the server ID.

  3. Enter the user name and password that you set when you deployed the AWS CloudFormation stack. If you kept the default options, the user name is myuser and the password is MySuperSecretPassword.

  4. Enter the server protocol and source IP address, if you set them when you deployed the AWS CloudFormation stack.

    If user authentication succeeds, the command returns a StatusCode: 200 HTML response and a JSON object containing the details of the user's roles and permissions, as shown in the following example. 

    {
    "Response": "{\"Policy\": \"{\n \"Version\": \"2012-10-17\",\n \"Statement\": [\n{\n \"Sid\": \"ReadAndListAllBuckets\",\n 
    \"Effect\": \"Allow\",\n \"Action\": [\n \"s3:ListAllMybuckets\",\n \"s3:GetBucketLocation\",\n \"s3:ListBucket\",\n 
    \"s3:GetObjectVersion\",\n \"s3:GetObjectVersion\"\n],\n \"Resource\":\"*\"\n}\n]\n}\",\"Role\": 
    \"arn:aws:iam::000000000000:role/MyUserS3AccessRole\",\"HomeDirectory\": \"/\"}",
    "StatusCode": 200,
    "Message": "",
    "Url": "https://abcde1234.execute-api.us-east-2.amazonaws.com/prod/servers/s-123a4567bcd891e23/users/myuser/config"
}

Implementing your API Gateway method

To create a custom identity provider for Transfer Family, your API Gateway method must implement a single method that has a resource path of /servers/serverId/users/username/config. The serverId and username values come from the RESTful resource path. Optionally, you can add the sourceIp and protocol values to the RESTful resource path.

Note

The user name must be a minimum of 3 and a maximum of 100 characters. You can use the following characters in the user name: a–z, A-Z, 0–9, underscore (_), hyphen (-), period (.), and at sign (@). However, the user name can't start with a hyphen (-), period (.), or at sign (@).

If Transfer Family attempts password authentication for your user, the service supplies a Password: header field. In the absence of a Password: header, Transfer Family attempts public key authentication to authenticate your user.

When you are using an identity provider to authenticate and authorize end users, in addition to validating their credentials, you can allow or deny access requests based on the IP addresses of the clients used by your end users. You can use this feature to ensure that data stored in your S3 buckets or your Amazon EFS file system can be accessed over the supported protocols only from IP addresses that you have specified as trusted. To enable this feature, you must include the sourceIp value in the RESTful resource path.

If you have multiple protocols enabled for your server and want to provide access using the same user name over multiple protocols, you can do so as long as the credentials specific to each protocol have been set up in your identity provider. To enable this feature, you must include the protocol value in the RESTful resource path.

Your API Gateway method should always return HTTP status code 200. Any other HTTP status code means that there was an error accessing the API.

Amazon S3 example response

The example response body is a JSON document of the following form for Amazon S3. 

{
 "Role": "IAM role with configured S3 permissions",
 "PublicKeys": [
     "ssh-rsa public-key1",
     "ssh-rsa public-key2"
  ],
 "Policy": "STS Assume role session policy",
 "HomeDirectory": "/bucketName/path/to/home/directory"
}
Note

The policy is escaped JSON as a string. For example: 


"Policy":
"{
  \"Version\": \"2012-10-17\",
  \"Statement\":
     [
     {\"Condition\":
        {\"StringLike\":
            {\"s3:prefix\":
               [\"user/*\", \"user/\"]}},
     \"Resource\": \"arn:aws:s3:::bucket\",
     \"Action\": \"s3:ListBucket\",
     \"Effect\": \"Allow\",
     \"Sid\": \"ListHomeDir\"},
     {\"Resource\": \"arn:aws:s3:::*\",
        \"Action\": [\"s3:PutObject\",
        \"s3:GetObject\",
        \"s3:DeleteObjectVersion\",
        \"s3:DeleteObject\",
        \"s3:GetObjectVersion\",
        \"s3:GetObjectACL\",
        \"s3:PutObjectACL\"],
     \"Effect\": \"Allow\",
     \"Sid\": \"HomeDirObjectAccess\"}]
}"

The following example reponse shows that a user has a Logical home directory type.

{
   "Role": "arn:aws:iam::123456789012:role/role-api-gateway-s3",
   "HomeDirectoryType": "LOGICAL",
   "HomeDirectoryDetails": "[{"Entry":"/","Target":"/my-home-bucket"}]",
   "PublicKeys": "[]"
}

Amazon EFS example response

The example response body is a JSON document of the following form for Amazon EFS. 

{
 "Role": "IAM role with configured EFS permissions",
 "PublicKeys": [
     "ssh-rsa public-key1",
     "ssh-rsa public-key2"
  ],
 "PosixProfile": {
   "Uid": "POSIX user ID",
   "Gid": "POSIX group ID",
   "SecondaryGids": [Optional list of secondary Group IDs],
 },
 "HomeDirectory": "/fs-id/path/to/home/directory"
}

The Role field shows that successful authentication occurred. When doing password authentication (when you supply a Password: header), you don't need to provide SSH public keys. If a user can't be authenticated, for example, if the password is incorrect, your method should return a response without Role set. An example of such a response is an empty JSON object.

The following example response shows a user that has a Logical home directory type. 

{
    "Role": "arn:aws:iam::123456789012:role/role-api-gateway-efs",
    "HomeDirectoryType": "LOGICAL",
    "HomeDirectoryDetails": "[{"Entry":"/","Target":"/fs-faa1a123"}]",
    "PublicKeys": "[]",
    "PosixProfile": "{Gid: 65534,Uid: 65534}"
    }

You can include user policies in the Lambda function in JSON format. For more information about configuring user policies in Transfer Family, see Managing access controls.

Example Lambda functions for authentication

To implement different authentication strategies, edit the Lambda function that your gateway uses. To help you meet your application's needs, you can use the following example Lambda functions in Node.js. For more information about Lambda, see the AWS Lambda Developer Guide or Building Lambda functions with Node.js.

Default Lambda function

The following Lambda function takes your user name, password (in the header field), IAM access role, public SSH key, and protocol. You can use the protocol field to look up your identity provider. Supported protocol values are SFTP, FTPS, and FTP.

Note

If you have multiple protocols enabled for your server and want to provide access using the same user name over multiple protocols, you can do so as long as the credentials specific to the protocol have been set up in your identity provider. For FTP, we recommend maintaining separate credentials from SFTP and FTPS. This is because, unlike SFTP and FTPS, FTP transmits credentials in clear text. By isolating FTP credentials from SFTP or FTPS, if FTP credentials are shared or exposed, your workloads using SFTP or FTPS remain secure.

The Lambda function authenticates the user, and, if successful, returns the relevant IAM access role and policy. This Lambda function is the same one that is used in the example AWS CloudFormation template.

The HomeDirectoryType parameter specifies the type of landing directory (folder) that you want your user's home directory to be when they log into the server. If you set this parameter to PATH, the user sees the absolute Amazon S3 bucket or Amazon EFS paths as is in their file transfer protocol clients. If you set this parameter to LOGICAL, you must provide mappings in the HomeDirectoryMappings parameter for how you want to make Amazon S3 or Amazon EFS paths visible to your users. 

// GetUserConfig Lambda

exports.handler = (event, context, callback) => {
  console.log("Username:", event.username, "ServerId: ", event.serverId);

  var response;
  // Check if the user name presented for authentication is correct. This doesn't check the value of the serverId, only that it is provided.
  // There is also event.protocol (one of "FTP", "FTPS", "SFTP") and event.sourceIp (e.g., "127.0.0.1") to further restrict logins.
  if (event.serverId !== "" && event.username == '${UserName}') {
    response = {
      Role: '${UserRoleArn}', // The user will be authenticated if and only if the Role field is not blank
      Policy: '', // Optional JSON blob to further restrict this user's permissions
      HomeDirectory: '${UserHomeDirectory}' // Not required, defaults to '/'
    };
    
    // Check if password is provided
    if (event.password == "") {
      // If no password provided, return the user's SSH public key
     response['PublicKeys'] = [ "${UserPublicKey1}" ];
    // Check if password is correct
    } else if (event.password !== '${UserPassword}') {
      // Return HTTP status 200 but with no role in the response to indicate authentication failure
      response = {};
    } 
  } else {
    // Return HTTP status 200 but with no role in the response to indicate authentication failure
    response = {};
  }
  callback(null, response);
};

The following Lambda function provides the details for a user that has a Logical home directory type. The user, role, Posix, password and home directroy details are all examples, and need to be replaced with your actual values. 

// GetUserConfig Lambda

exports.handler = (event, context, callback) => {
  console.log("Username:", event.username, "ServerId: ", event.serverId);

  var response;
  // Check if the username presented for authentication is correct. This doesn't check the value of the serverId, only that it is provided.
  if (event.serverId !== "" && event.username == 'example-user') {
    response = {
      Role: 'arn:aws:iam::123456789012:role/role-api-gateway', // The user will be authenticated if and only if the Role field is not blank
      PosixProfile: {"Gid": 65534, "Uid": 65534},
      HomeDirectoryDetails: "[{\"Entry\": \"/\", \"Target\": \"/fs-faa1a123\"}]",
      HomeDirectoryType: "LOGICAL",
      //HomeDirectory: '/fs-faa1a123' // Not required, defaults to '/'
    };

    // Check if password is provided
    if (event.password == "") {
      // If no password provided, return the user's SSH public key
      response['PublicKeys'] = [ "" ];
    // Check if password is correct
    } else if (event.password !== 'Password1234') {
      // Return HTTP status 200 but with no role in the response to indicate authentication failure
      response = {};
    }
  } else {
    // Return HTTP status 200 but with no role in the response to indicate authentication failure
    response = {};
  }
  callback(null, response);
};

Lambda function for use with AWS Secrets Manager

To use AWS Secrets Manager as your identity provider, you can work with the Lambda function in the sample AWS CloudFormation template. The Lambda function queries the Secrets Manager service with your credentials and, if successful, returns a designated secret. For more information about Secrets Manager, see the AWS Secrets Manager User Guide.

To download a sample AWS CloudFormation template that uses this Lambda function, go to the Amazon S3 bucket provided by AWS Transfer Family.