Post Syndicated from Faraz Angabini original https://aws.amazon.com/blogs/security/extend-aws-iam-roles-to-workloads-outside-of-aws-with-iam-roles-anywhere/

AWS Identity and Access Management (IAM) has now made it easier for you to use IAM roles for your workloads that are running outside of AWS, with the release of IAM Roles Anywhere. This feature extends the capabilities of IAM roles to workloads outside of AWS. You can use IAM Roles Anywhere to provide a secure way for on-premises servers, containers, or applications to obtain temporary AWS credentials and remove the need for creating and managing long-term AWS credentials.

In this post, I will briefly discuss how IAM Roles Anywhere works. I’ll mention some of the common use cases for IAM Roles Anywhere. And finally, I’ll walk you through an example scenario to demonstrate how the implementation works.

Background

To enable your applications to access AWS services and resources, you need to provide the application with valid AWS credentials for making AWS API requests. For workloads running on AWS, you do this by associating an IAM role with Amazon Elastic Compute Cloud (Amazon EC2), Amazon Elastic Container Service (Amazon ECS), Amazon Elastic Kubernetes Service (Amazon EKS), or AWS Lambda resources, depending on the compute platform hosting your application. This is secure and convenient, because you don’t have to distribute and manage AWS credentials for applications running on AWS. Instead, the IAM role supplies temporary credentials that applications can use when they make AWS API calls.

IAM Roles Anywhere enables you to use IAM roles for your applications outside of AWS to access AWS APIs securely, the same way that you use IAM roles for workloads on AWS. With IAM Roles Anywhere, you can deliver short-term credentials to your on-premises servers, containers, or other compute platforms. When you use IAM Roles Anywhere to vend short-term credentials you can remove the need for long-term AWS access keys and secrets, which can help improve security, and remove the operational overhead of managing and rotating the long-term credentials. You can also use IAM Roles Anywhere to provide a consistent experience for managing credentials across hybrid workloads.

In this post, I assume that you have a foundational knowledge of IAM, so I won’t go into the details here about IAM roles. For more information on IAM roles, see the IAM documentation.

How does IAM Roles Anywhere work?

IAM Roles Anywhere relies on public key infrastructure (PKI) to establish trust between your AWS account and certificate authority (CA) that issues certificates to your on-premises workloads. Your workloads outside of AWS use IAM Roles Anywhere to exchange X.509 certificates for temporary AWS credentials. The certificates are issued by a CA that you register as a trust anchor (root of trust) in IAM Roles Anywhere. The CA can be part of your existing PKI system, or can be a CA that you created with AWS Certificate Manager Private Certificate Authority (ACM PCA).

Your application makes an authentication request to IAM Roles Anywhere, sending along its public key (encoded in a certificate) and a signature signed by the corresponding private key. Your application also specifies the role to assume in the request. When IAM Roles Anywhere receives the request, it first validates the signature with the public key, then it validates that the certificate was issued by a trust anchor previously configured in the account. For more details, see the signature validation documentation.

After both validations succeed, your application is now authenticated and IAM Roles Anywhere will create a new role session for the role specified in the request by calling AWS Security Token Service (AWS STS). The effective permissions for this role session are the intersection of the target role’s identity-based policies and the session policies, if specified, in the profile you create in IAM Roles Anywhere. Like any other IAM role session, it is also subject to other policy types that you might have in place, such as permissions boundaries and service control policies (SCPs).

There are typically three main tasks, performed by different personas, that are involved in setting up and using IAM Roles Anywhere:

• Initial configuration of IAM Roles Anywhere – This task involves creating a trust anchor, configuring the trust policy of the role that IAM Roles Anywhere is going to assume, and defining the role profile. These activities are performed by the AWS account administrator and can be limited by IAM policies.
• Provisioning of certificates to workloads outside AWS – This task involves ensuring that the X.509 certificate, signed by the CA, is installed and available on the server, container, or application outside of AWS that needs to authenticate. This is performed in your on-premises environment by an infrastructure admin or provisioning actor, typically by using existing automation and configuration management tools.
• Using IAM Roles Anywhere – This task involves configuring the credential provider chain to use the IAM Roles Anywhere credential helper tool to exchange the certificate for session credentials. This is typically performed by the developer of the application that interacts with AWS APIs.

I’ll go into the details of each task when I walk through the example scenario later in this post.

Common use cases for IAM Roles Anywhere

You can use IAM Roles Anywhere for any workload running in your data center, or in other cloud providers, that requires credentials to access AWS APIs. Here are some of the use cases we think will be interesting to customers based on the conversations and patterns we have seen:

• Back up on-premises data to Amazon Simple Storage Service (Amazon S3)
• Provide on-premises Kubernetes workloads access to native AWS services such as Amazon DynamoDB and Amazon Simple Queue Service (Amazon SQS)
• Access secrets stored in AWS Secrets Manager from workloads outside AWS
• Send security findings from on-premises sources to AWS Security Hub
• Enable hybrid workloads to access AWS services over the course of phased migrations

Example scenario and walkthrough

To demonstrate how IAM Roles Anywhere works in action, let’s walk through a simple scenario where you want to call S3 APIs to upload some data from a server in your data center.

Prerequisites

Before you set up IAM Roles Anywhere, you need to have the following requirements in place:

• The certificate bundle of your own CA, or an active ACM PCA CA in the same AWS Region as IAM Roles Anywhere
• An end-entity certificate and associated private key available on the on-premises server
• Administrator permissions for IAM roles and IAM Roles Anywhere

Setup

Here I demonstrate how to perform the setup process by using the IAM Roles Anywhere console. Alternatively, you can use the AWS API or Command Line Interface (CLI) to perform these actions. There are three main activities here:

• Create a trust anchor
• Create and configure a role that trusts IAM Roles Anywhere
• Create a profile

To create a trust anchor

1. Navigate to the IAM Roles Anywhere console.
2. Under Trust anchors, choose Create a trust anchor.
3. On the Create a trust anchor page, enter a name for your trust anchor and select the existing AWS Certificate Manager Private CA from the list. Alternatively, if you want to use your own external CA, choose External certificate bundle and provide the certificate bundle.

Figure 1: Create a trust anchor in IAM Roles Anywhere

To create and configure a role that trusts IAM Roles Anywhere

1. Using the AWS Command Line Interface (AWS CLI), you are going to create an IAM role with appropriate permissions that you want your on-premises server to assume after authenticating to IAM Roles Anywhere. Save the following trust policy as rolesanywhere-trust-policy.json on your computer.

   {
       "Version": "2012-10-17",
       "Statement": [
           {
               "Effect": "Allow",
               "Principal": {
                   "Service": "rolesanywhere.amazonaws.com"
               },
               "Action": [
                   "sts:AssumeRole",
                   "sts:SetSourceIdentity",
                   "sts:TagSession"
               ]
           }
       ]
   }

2. Save the following identity-based policy as onpremsrv-permissions-policy.json. This grants the role permissions to write objects into the specified S3 bucket.

   {
       "Version": "2012-10-17",
       "Statement": [
           {
               "Effect": "Allow",
               "Action": "s3:PutObject",
               "Resource": "arn:aws:s3:::<DOC-EXAMPLE-BUCKET>/*"
           }
       ]
   }

3. Run the following two AWS CLI commands to create the role and attach the permissions policy.

   aws iam create-role \
   --role-name ExampleS3WriteRole \
   --assume-role-policy-document file://<path>/rolesanywhere-trust-policy.json
   
   
   
   aws iam put-role-policy \
   --role-name ExampleS3WriteRole \
   --policy-name onpremsrv-inline-policy \
   --policy-document file://<path>/onpremsrv-permissions-policy.json

You can optionally use condition statements based on the attributes extracted from the X.509 certificate to further restrict the trust policy to control the on-premises resources that can obtain credentials from IAM Roles Anywhere. IAM Roles Anywhere sets the SourceIdentity value to the CN of the subject (onpremsrv01 in my example). It also sets individual session tags (PrincipalTag/) with the derived attributes from the certificate. So, you can use the principal tags in the Condition clause in the trust policy as additional authorization constraints.

For example, the Subject for the certificate I use in this post is as follows.

Subject: … O = Example Corp., OU = SecOps, CN = onpremsrv01

So, I can add condition statements like the following into the trust policy (rolesanywhere-trust-policy.json):

...
    "Condition": {
        "StringEquals": {
            "aws:PrincipalTag/x509Subject/CN": "onpremsrv01",
            "aws:PrincipalTag/x509Subject/OU": "SecOps"
        }
    }
...

To learn more, see the trust policy for IAM Roles Anywhere documentation.

To create a profile

1. Navigate to the Roles Anywhere console.
2. Under Profiles, choose Create a profile.
3. On the Create a profile page, enter a name for the profile.
4. For Roles, select the role that you created in the previous step (ExampleS3WriteRole).
5. 5. Optionally, you can define session policies to further scope down the sessions delivered by IAM Roles Anywhere. This is particularly useful when you configure the profile with multiple roles and want to restrict permissions across all the roles. You can add the desired session polices as managed policies or inline policy. Here, for demonstration purpose, I add an inline policy to only allow requests coming from my specified IP address.

Figure 2: Create a profile in IAM Roles Anywhere

At this point, IAM Roles Anywhere setup is complete and you can start using it.

Use IAM Roles Anywhere

IAM Roles Anywhere provides a credential helper tool that can be used with the process credentials functionality that all current AWS SDKs support. This simplifies the signing process for the applications. See the IAM Roles Anywhere documentation to learn how to get the credential helper tool.

To test the functionality first, run the credential helper tool (aws_signing_helper) manually from the on-premises server, as follows.

./aws_signing_helper credential-process \
    --certificate /path/to/certificate.pem \
    --private-key /path/to/private-key.pem \
    --trust-anchor-arn <TA_ARN> \
    --profile-arn <PROFILE_ARN> \
    --role-arn <ExampleS3WriteRole_ARN>

Figure 3: Running the credential helper tool manually

You should successfully receive session credentials from IAM Roles Anywhere, similar to the example in Figure 3. Once you’ve confirmed that the setup works, update or create the ~/.aws/config file and add the signing helper as a credential_process. This will enable unattended access for the on-premises server. To learn more about the AWS CLI configuration file, see Configuration and credential file settings.

# ~/.aws/config content
[default]
 credential_process = ./aws_signing_helper credential-process
    --certificate /path/to/certificate.pem
    --private-key /path/to/private-key.pem
    --trust-anchor-arn <TA_ARN>
    --profile-arn <PROFILE_ARN>
    --role-arn <ExampleS3WriteRole_ARN>

To verify that the config works as expected, call the aws sts get-caller-identity AWS CLI command and confirm that the assumed role is what you configured in IAM Roles Anywhere. You should also see that the role session name contains the Serial Number of the certificate that was used to authenticate (cc:c3:…:85:37 in this example). Finally, you should be able to copy a file to the S3 bucket, as shown in Figure 4.

Figure 4: Verify the assumed role

Audit

As with other AWS services, AWS CloudTrail captures API calls for IAM Roles Anywhere. Let’s look at the corresponding CloudTrail log entries for the activities we performed earlier.

The first log entry I’m interested in is CreateSession, when the on-premises server called IAM Roles Anywhere through the credential helper tool and received session credentials back.

{
    ...
    "eventSource": "rolesanywhere.amazonaws.com",
    "eventName": "CreateSession",
    ...
    "requestParameters": {
        "cert": "MIICiTCCAfICCQD6...mvw3rrszlaEXAMPLE",
        "profileArn": "arn:aws:rolesanywhere:us-west-2:111122223333:profile/PROFILE_ID",
        "roleArn": "arn:aws:iam::111122223333:role/ExampleS3WriteRole",
        ...
    },
    "responseElements": {
        "credentialSet": [
        {
            "assumedRoleUser": {
                "arn": "arn:aws:sts::111122223333:assumed-role/ExampleS3WriteRole/00ccc3a2432f8c5fec93f0fc574f118537",
            },
            "credentials": {
                ...
            },
            ...
            "sourceIdentity": "CN=onpremsrv01"
        }
      ],
    },
    ...
}

You can see that the cert, along with other parameters, is sent to IAM Roles Anywhere and a role session along with temporary credentials is sent back to the server.

The next log entry we want to look at is the one for the s3:PutObject call we made from our on-premises server.

{
    ...
    "eventSource": "s3.amazonaws.com",
    "eventName": "PutObject",
    "userIdentity":{
        "type": "AssumedRole",
        "arn": "arn:aws:sts::111122223333:assumed-role/ExampleS3WriteRole/00ccc3a2432f8c5fec93f0fc574f118537",
        ...
        "sessionContext":
        {
            ...
            "sourceIdentity": "CN=onpremsrv01"
        },
    },
    ...
}

In addition to the CloudTrail logs, there are several metrics and events available for you to use for monitoring purposes. To learn more, see Monitoring IAM Roles Anywhere.

Additional notes

You can disable the trust anchor in IAM Roles Anywhere to immediately stop new sessions being issued to your resources outside of AWS. Certificate revocation is supported through the use of imported certificate revocation lists (CRLs). You can upload a CRL that is generated from your CA, and certificates used for authentication will be checked for their revocation status. IAM Roles Anywhere does not support callbacks to CRL Distribution Points (CDPs) or Online Certificate Status Protocol (OCSP) endpoints.

Another consideration, not specific to IAM Roles Anywhere, is to ensure that you have securely stored the private keys on your server with appropriate file system permissions.

Conclusion

In this post, I discussed how the new IAM Roles Anywhere service helps you enable workloads outside of AWS to interact with AWS APIs securely and conveniently. When you extend the capabilities of IAM roles to your servers, containers, or applications running outside of AWS you can remove the need for long-term AWS credentials, which means no more distribution, storing, and rotation overheads.

I mentioned some of the common use cases for IAM Roles Anywhere. You also learned about the setup process and how to use IAM Roles Anywhere to obtain short-term credentials.

 
If you have any questions, you can start a new thread on AWS re:Post or reach out to AWS Support.