Tag Archives: AWS STS

Create fine-grained session permissions using IAM managed policies

Post Syndicated from Sulay Shah original https://aws.amazon.com/blogs/security/create-fine-grained-session-permissions-using-iam-managed-policies/

As a security best practice, AWS Identity and Access Management (IAM) recommends that you use temporary security credentials from AWS Security Token Service (STS) when you access your AWS resources. Temporary credentials are short-term credentials generated dynamically and provided to the user upon request. Today, one of the most widely used mechanisms for requesting temporary credentials in AWS is an IAM role. The advantage of using an IAM role is that multiple users in your organization can assume the same IAM role. By default, all users assuming the same role get the same permissions for their role session. To create distinctive role session permissions or to further restrict session permissions, users or systems can set a session policy when assuming a role. A session policy is an inline permissions policy which users pass in the session when they assume the role. You can pass the policy yourself, or you can configure your broker to insert the policy when your identities federate in to AWS (if you have an identity broker configured in your environment). This allows your administrators to reduce the number of roles they need to create, since multiple users can assume the same role yet have unique session permissions. If users don’t require all the permissions associated to the role to perform a specific action in a given session, your administrator can configure the identity broker to pass a session policy to reduce the scope of session permissions when users assume the role. This helps administrators set permissions for users to perform only those specific actions for that session.

With today’s launch, AWS now enables you to specify multiple IAM managed policies as session policies when users assume a role. This means you can use multiple IAM managed policies to create fine-grained session permissions for your user’s sessions. Additionally, you can centrally manage session permissions using IAM managed policies.
In this post, I review session policies and their current capabilities, introduce the concept of using IAM managed policies as session policies to control session permissions, and show you how to use managed policies to create fine-grained session permissions in AWS.

How do session policies work?

Before I walk through an example, I’ll review session policies.

A session policy is an inline policy that you can create on the fly and pass in the session during role assumption to further scope the permissions of the role session. The effective permissions of the session are the intersection of the role’s identity-based policies and the session policy. The maximum permissions that a session can have are the permissions that are allowed by the role’s identity-based policies. You can pass a single inline session policy programmatically by using the policy parameter with the AssumeRole, AssumeRoleWithSAML, AssumeRoleWithWebIdentity, and GetFederationToken API operations.

Next, I’ll provide an example with an inline session policy to demonstrate how you can restrict session permissions.

Example: Passing a session policy with AssumeRole API to restrict session permissions

Consider a scenario where security administrator John has administrative privileges when he assumes the role SecurityAdminAccess in the organization’s AWS account. When John assumes this role, he knows the specific actions he’ll perform using this role. John is cautious of the role permissions and follows the practice of restricting his own permissions by using a session policy when assuming the role. This way, John ensures that at any given point in time, his role session can only perform the specific action for which he assumed the SecurityAdminAccess role.

In my example, John only needs permissions to access an Amazon Simple Storage Service (S3) bucket called NewHireOrientation in the same account. He passes a session policy using the policy.json file below to reduce his session permissions when assuming the role SecurityAdminAccess.

    "Action":["s3:GetBucket", "s3:GetObject"],
    "Resource": ["arn:aws:s3:::NewHireOrientation", "arn:aws:s3:::NewHireOrientation/*"]

In this example, the action and resources elements of the policy statement allow access only to the NewHireOrientation bucket and all the objects inside this bucket.

Using the AWS Command Line Interface (AWS CLI), John can pass the session policy’s file path (that is, file://policy.json) while calling the AssumeRole API with the following commands:

aws sts assume-role 
--role-arn "arn:aws:iam::111122223333:role/SecurityAdminAccess" 
--role-session-name "s3-session" 
--policy file://policy.json 

When John assumes the SecurityAdminAccess role using the above command, his effective session permissions are the intersection of the permissions on the role and the session policy. This means that although the SecurityAdminAccess role had administrative privileges, John’s resulting session permissions are s3:GetBucket and s3:GetObject on the NewHireOrientation bucket. This way, John can ensure he only has access to the NewHireOrientation bucket for this session.

Using IAM managed policies as session policies

You can now pass up to 10 IAM managed policies as session policies. This gives you the ability to further restrict session permissions. The managed policy you pass can be AWS managed or customer managed. To pass managed policies as session policies, you need to specify the Amazon Resource Name (ARN) of the IAM policies using the new policy-arns parameter in the AssumeRole, AssumeRoleWithSAML, AssumeRoleWithWebIdentity, or GetFederationToken API operations. You can use existing managed policies or create new policies in your account and pass them as session policies with any of the aforementioned APIs. The managed policies passed in the role session must be in the same account as that of the role. Additionally, you can pass an inline session policy and ARNs of managed policies in the same role session. To learn more about the sizing guidelines for session policies, please review the STS documentation.

Next, I’ll provide an example using IAM managed policies as session policies to help you understand how you can use multiple managed policies to create fine-grained session permissions.

Example: Passing IAM managed policies in a role session

Consider an example where Mary has a software development team in California (us-west-1) working on a project using Amazon Elastic Compute Cloud (EC2). This team needs permissions to spin up new EC2 instances to meet the project’s scalability requirements. Mary’s organization has a security policy that requires developers to create and manage AWS resources in their respective geographic locations only. This means a developer from California should have permissions to launch new EC2 instances only in California. Now, Mary’s organization has an identity and authentication system such as Active Directory, for which all employees already have identities created. Additionally, there is a custom identity broker application which verifies that employees are signed into the existing identity and authentication system. This broker application is configured to obtain temporary security credentials for the employees using the AssumeRole API. (To learn more about using identity provider and identity broker with AWS, please see AWS Federated Authentication with Active Directory Federation Services..)

Mary creates a managed policy called DevCalifornia and adds a region restriction for California using the aws:RequestedRegion condition key. Following the best practice of granting least privilege, Mary lists out the specific actions the developers would need for spinning up EC2 instances:

    "Version": "2012-10-17",
    "Statement": [
            "Effect": "Allow",
            "Action": [
            "Resource": "*",
                    "Condition": {
                "StringEquals": {
                    "aws:RequestedRegion": "us-west-1"

The above policy grants specific permissions to launch EC2 instances. The condition element of the policy sets a restriction on the Region where these actions can be performed. The condition key aws:RequestedRegion ensures that these service-specific actions can only be performed in California.

For Mary’s team’s use case, instead of creating a new role Mary uses an existing role in her account called EC2Admin, which has the AmazonEC2FullAccess AWS managed policy attached to it, granting full access to Amazon EC2. Next, Mary configures the identity broker in such a way that the developers from the team in California can assume the EC2Admin role but with reduced session permissions. The broker passes the DevCalifornia managed policy as a session policy to reduce the scope of the session permissions when a developer from Mary’s team assumes the role. This way, Mary can ensure the team remains compliant with her organization’s security policy.

If performed using the AWS CLI, the command would look like this:

aws sts assume-role –role-arn “arn:aws:iam::444455556666:role/AppDev” –role-session-name “teamCalifornia-session” –policy-arns arn=”arn:aws:iam::444455556666:policy/DevCalifornia”

If you want to pass multiple managed policies as session policies, then the command would look like this:

aws sts assume-role –role-arn “arn:aws:iam::<accountID>:role/<RoleName>” –role-session-name “<example-session>” –policy-arns arn=”arn:aws:iam::<accountID>:policy/<PolicyName1>” arn=”arn:aws:iam::<accountID>:policy/<PolicyName2>”

In the above example, PolicyName1 and PolicyName2 can be AWS managed or customer managed policies. You can also use them in conjunction, where PolicyName1 is an AWS managed policy and PolicyName2 a customer managed policy.


You can now use IAM managed policies as session policies in role sessions and federated sessions to create fine-grained session permissions. You can use this functionality today by creating IAM managed policies using your existing inline session policies and referencing their policy ARNs in your role sessions. You can also keep using your existing session policy and pass the ARNs of IAM managed policies using the new policy-arn parameter to further scope your session permissions.

If you have comments about this post, submit them in the Comments section below. If you have questions about or suggestions for this solution, start a new thread on the IAM forum.

Sulay Shah

Sulay is the product manager for Identity and Access Management service at AWS. He strongly believes in the customer first approach and is always looking for new opportunities to assist customers. Outside of work, Sulay enjoys playing soccer and watching movies. Sulay holds a master’s degree in computer science from the North Carolina State University.

Secure API Access with Amazon Cognito Federated Identities, Amazon Cognito User Pools, and Amazon API Gateway

Post Syndicated from Ed Lima original https://aws.amazon.com/blogs/compute/secure-api-access-with-amazon-cognito-federated-identities-amazon-cognito-user-pools-and-amazon-api-gateway/

Ed Lima, Solutions Architect


Our identities are what define us as human beings. Philosophical discussions aside, it also applies to our day-to-day lives. For instance, I need my work badge to get access to my office building or my passport to travel overseas. My identity in this case is attached to my work badge or passport. As part of the system that checks my access, these documents or objects help define whether I have access to get into the office building or travel internationally.

This exact same concept can also be applied to cloud applications and APIs. To provide secure access to your application users, you define who can access the application resources and what kind of access can be granted. Access is based on identity controls that can confirm authentication (AuthN) and authorization (AuthZ), which are different concepts. According to Wikipedia:


The process of authorization is distinct from that of authentication. Whereas authentication is the process of verifying that “you are who you say you are,” authorization is the process of verifying that “you are permitted to do what you are trying to do.” This does not mean authorization presupposes authentication; an anonymous agent could be authorized to a limited action set.

Amazon Cognito allows building, securing, and scaling a solution to handle user management and authentication, and to sync across platforms and devices. In this post, I discuss the different ways that you can use Amazon Cognito to authenticate API calls to Amazon API Gateway and secure access to your own API resources.


Amazon Cognito Concepts


It’s important to understand that Amazon Cognito provides three different services:

Today, I discuss the use of the first two. One service doesn’t need the other to work; however, they can be configured to work together.

Amazon Cognito Federated Identities

To use Amazon Cognito Federated Identities in your application, create an identity pool. An identity pool is a store of user data specific to your account. It can be configured to require an identity provider (IdP) for user authentication, after you enter details such as app IDs or keys related to that specific provider.

After the user is validated, the provider sends an identity token to Amazon Cognito Federated Identities. In turn, Amazon Cognito Federated Identities contacts the AWS Security Token Service (AWS STS) to retrieve temporary AWS credentials based on a configured, authenticated IAM role linked to the identity pool. The role has appropriate IAM policies attached to it and uses these policies to provide access to other AWS services.

Amazon Cognito Federated Identities currently supports the IdPs listed in the following graphic.


Continue reading Secure API Access with Amazon Cognito Federated Identities, Amazon Cognito User Pools, and Amazon API Gateway

The Top 20 Most Viewed AWS IAM Documentation Pages in 2016

Post Syndicated from Dave Bishop original https://aws.amazon.com/blogs/security/the-top-20-most-viewed-aws-iam-documentation-pages-in-2016/

The following 20 pages were the most viewed AWS Identity and Access Management (IAM) documentation pages in 2016. I have included a brief description with each link to give you a clearer idea of what each page covers. Use this list to see what other people have been viewing and perhaps to pique your own interest about a topic you’ve been meaning to research.

  1. What Is IAM?
    IAM is a web service that helps you securely control access to AWS resources for your users. You use IAM to control who can use your AWS resources (authentication) and what resources they can use and in what ways (authorization).
  2. Creating an IAM User in Your AWS Account
    You can create one or more IAM users in your AWS account. You might create an IAM user when someone joins your organization, or when you have a new application that needs to make API calls to AWS.
  3. The IAM Console and the Sign-in Page
    This page provides information about the IAM-enabled AWS Management Console sign-in page and explains how to create a unique sign-in URL for your account.
  4. How Users Sign In to Your Account
    After you create IAM users and passwords for each, users can sign in to the AWS Management Console for your AWS account with a special URL.
  5. IAM Best Practices
    To help secure your AWS resources, follow these recommendations for IAM.
  6. IAM Policy Elements Reference
    This page describes the elements that you can use in an IAM policy. The elements are listed here in the general order you use them in a policy.
  7. Managing Access Keys for IAM Users
    Users need their own access keys to make programmatic calls to AWS from the AWS Command Line Interface (AWS CLI), Tools for Windows PowerShell, the AWS SDKs, or direct HTTP calls using the APIs for individual AWS services. To fill this need, you can create, modify, view, or rotate access keys (access key IDs and secret access keys) for IAM users.
  8. Working with Server Certificates
    Some AWS services can use server certificates that you manage with IAM or AWS Certificate Manager (ACM). In many cases, we recommend that you use ACM to provision, manage, and deploy your SSL/TLS certificates.
  9. Your AWS Account ID and Its Alias
    Learn how to find your AWS account ID number and its alias.
  10. Overview of IAM Policies
    This page provides an overview of IAM policies. A policy is a document that formally states one or more permissions.
  11. Using Multi-Factor Authentication (MFA) in AWS
    For increased security, we recommend that you configure MFA to help protect your AWS resources. MFA adds extra security because it requires users to enter a unique authentication code from an approved authentication device or SMS text message when they access AWS websites or services.
  12. Example Policies for Administering AWS Resources
    This page shows some examples of policies that control access to resources in AWS services.
  13. Using an IAM Role to Grant Permissions to Applications Running on Amazon EC2 Instances
    Use an IAM role to manage temporary credentials for applications that run on an EC2 instance. When you use a role, you do not have to distribute long-term credentials to an EC2 instance. Instead, the role supplies temporary permissions that applications can use when they make calls to other AWS resources.
  14. IAM Roles
    An IAM role is similar to a user, in that it is an AWS identity with permission policies that determine what the identity can and cannot do in AWS. However, instead of being uniquely associated with one person, a role is intended to be assumable by anyone who needs it.
  15. Enabling a Virtual MFA Device
    A virtual MFA device uses a software application to generate a six-digit authentication code that is compatible with the time-based one-time password (TOTP) standard, as described in RFC 6238. The app can run on mobile hardware devices, including smartphones.
  16. Creating Your First IAM Admin User and Group
    This procedure describes how to create an IAM group named Administrators, grant the group full permissions for all AWS services, and then create an administrative IAM user for yourself by adding the user to the Administrators group.
  17. Using Instance Profiles
    An instance profile is a container for an IAM role that you can use to pass role information to an EC2 instance when the instance starts.
  18. Working with Server Certificates
    After you obtain or create a server certificate, you upload it to IAM so that other AWS services can use it. You might also need to get certificate information, rename or delete a certificate, or perform other management tasks.
  19. Temporary Security Credentials
    You can use the AWS Security Token Service (AWS STS) to create and provide trusted users with temporary security credentials that can control access to your AWS resources. Temporary security credentials work almost identically to the long-term access key credentials that your IAM users can use.
  20. Setting an Account Password Policy for IAM Users
    You can set a password policy on your AWS account to specify complexity requirements and mandatory rotation periods for your IAM users’ passwords.

In the “Comments” section below, let us know if you would like to see anything on these or other IAM documentation pages expanded or updated to make the documentation more useful for you.

– Dave

SAML Identity Federation: Follow-Up Questions, Materials, Guides, and Templates from an AWS re:Invent 2016 Workshop (SEC306)

Post Syndicated from Quint Van Deman original https://aws.amazon.com/blogs/security/saml-identity-federation-follow-up-questions-materials-guides-and-templates-from-an-aws-reinvent-2016-workshop-sec306/

As part of the re:Source Mini Con for Security Services at AWS re:Invent 2016, we conducted a workshop focused on Security Assertion Markup Language (SAML) identity federation: Choose Your Own SAML Adventure: A Self-Directed Journey to AWS Identity Federation Mastery. As part of this workshop, attendees were able to submit their own federation-focused questions to a panel of AWS experts. In this post, I share the questions and answers from that workshop because this information can benefit any AWS customer interested in identity federation.

I have also made available the full set of workshop materials, lab guides, and AWS CloudFormation templates. I encourage you to use these materials to enrich your exploration of SAML for use with AWS.

Q: SAML assertions are limited to 50,000 characters. We often hit this limit by being in too many groups. What can AWS do to resolve this size-limit problem?

A: Because the SAML assertion is ultimately part of an API call, an upper bound must be in place for the assertion size.

On the AWS side, your AWS solution architect can log a feature request on your behalf to increase the maximum size of the assertion in a future release. The AWS service teams use these feature requests, in conjunction with other avenues of customer feedback, to plan and prioritize the features they deliver. To facilitate this process you need two things: the proposed higher value to which you’d like to see the maximum size raised, and a short written description that would help us understand what this increased limit would enable you to do.

On the AWS customer’s side, we often find that these cases are most relevant to centralized cloud teams that have broad, persistent access across many roles and accounts. This access is often necessary to support troubleshooting or simply as part of an individual’s job function. However, in many cases, exchanging persistent access for just-in-time access enables the same level of access but with better levels of visibility, reduced blast radius, and better adherence to the principle of least privilege. For example, you might implement a fast, efficient, and monitored workflow that allows you to provision a user into the necessary backend directory group for a short duration when needed in lieu of that user maintaining all of those group memberships on a persistent basis. This approach could effectively resolve the limit issue you are facing.

Q: Can we use OpenID Connect (OIDC) for federated authentication and authorization into the AWS Management Console? If so, does it have a similar size limit?

A: Currently, AWS support for OIDC is oriented around providing access to AWS resources from mobile or web applications, not access to the AWS Management Console. This is possible to do, but it requires the construction of a custom identity broker. In this solution, this broker would consume the OIDC identity, use its own logic to authenticate and authorize the user (thus being subject only to any size limits you enforce on the OIDC side), and use the sts:GetFederatedToken call to vend the user an AWS Security Token Service (STS) token for either AWS Management Console use or API/CLI use. During this sts:GetFederatedToken call, you attach a scoping policy with a limit of 2,048 characters. See Creating a URL that Enables Federated Users to Access the AWS Management Console (Custom Federation Broker) for additional details about custom identity brokers.

Q: We want to eliminate permanent AWS Identity and Access Management (IAM) access keys, but we cannot do so because of third-party tools. We are contemplating using HashiCorp Vault to vend permanent keys. Vault lets us tie keys to LDAP identities. Have you seen this work elsewhere? Do you think it will work for us?

A: For third-party tools that can run within Amazon EC2, you should use EC2 instance profiles to eliminate long-term credentials and their associated management (distribution, rotation, etc.). For third-party tools that cannot run within EC2, most customers opt to leverage their existing secrets-management tools and processes for the long-lived keys. These tools are often enhanced to make use of AWS APIs such as iam:GetCredentialReport (rotation information) and iam:{Create,Update,Delete}AccessKey (rotation operations). HashiCorp Vault is a popular tool with an available AWS Quick Start Reference Deployment, but any secrets management platform that is able to efficiently fingerprint the authorized resources and is extensible to work with the previously mentioned APIs will fill this need for you nicely.

Q: Currently, we use an Object Graph Navigation Library (OGNL) script in our identity provider (IdP) to build role Amazon Resource Names (ARNs) for the role attribute in the SAML assertion. The script consumes a list of distribution list display names from our identity management platform of which the user is a member. There is a 60-character limit on display names, which leaves no room for IAM pathing (which has a 512-character limit). We are contemplating a change. The proposed solution would make AWS API calls to get role ARNs from the AWS APIs. Have you seen this before? Do you think it will work? Does the AWS SAML integration support full-length role ARNs that would include up to 512 characters for the IAM path?

A: In most cases, we recommend that you use regular expression-based transformations within your IdP to translate a list of group names to a list of role ARNs for inclusion in the SAML assertion. Without pathing, you need to know the 12-digit AWS account number and the role name in order to be able to do so, which is accomplished using our recommended group-naming convention (AWS-Acct#-RoleName). With pathing (because “/” is not a valid character for group names within most directories), you need an additional source from which to pull this third data element. This could be as simple as an extra dimension in the group name (such as AWS-Acct#-Path-RoleName); however, that would multiply the number of groups required to support the solution. Instead, you would most likely derive the path element from a user attribute, dynamic group information, or even an external information store. It should work as long as you can reliably determine all three data elements for the user.

We do not recommend drawing the path information from AWS APIs, because the logic within the IdP is authoritative for the user’s authorization. In other words, the IdP should know for which full path role ARNs the user is authorized without asking AWS. You might consider using the AWS APIs to validate that the role actually exists, but that should really be an edge case. This is because you should integrate any automation that builds and provisions the roles with the frontend authorization layer. This way, there would never be a case in which the IdP authorizes a user for a role that doesn’t exist. AWS SAML integration supports full-length role ARNs.

Q: Why do AWS STS tokens contain a session token? This makes them incompatible with third-party tools that only support permanent keys. Is there a way to get rid of the session token to make temporary keys that contain only the access_key and the secret_key components?

A: The session token contains information that AWS uses to confirm that the AWS STS token is valid. There is no way to create a token that does not contain this third component. Instead, the preferred AWS mechanisms for distributing AWS credentials to third-party tools are EC2 instance profiles (in EC2), IAM cross-account trust (SaaS), or IAM access keys with secrets management (on-premises). Using IAM access keys, you can rotate the access keys as often as the third-party tool and your secrets management platform allow.

Q: How can we use SAML to authenticate and authorize code instead of having humans do the work? One proposed solution is to use our identity management (IDM) platform to generate X.509 certificates for identities, and then present these certificates to our IdP in order to get valid SAML assertions. This could then be included in an sts:AssumeRoleWithSAML call. Have you seen this working before? Do you think it will work for us?

A: Yes, when you receive a SAML assertion from your IdP by using your desired credential form (user name/password, X.509, etc.), you can use the sts:AssumeRoleWithSAML call to retrieve an AWS STS token. See How to Implement a General Solution for Federated API/CLI Access Using SAML 2.0 for a reference implementation.

Q: As a follow-up to the previous question, how can we get code using multi-factor authentication (MFA)? There is a gauth project that uses NodeJS to generate virtual MFAs. Code could theoretically get MFA codes from the NodeJS gauth server.

A: The answer depends on your choice of IdP and MFA provider. Generically speaking, you need to authenticate (either web-based or code-based) to the IdP using all of your desired factors before the SAML assertion is generated. This assertion can then include details of the authentication mechanism used as an additional attribute in role-assumption conditions within the trust policy in AWS. This lab guide from the workshop provides further details and a how-to guide for MFA-for-SAML.

This blog post clarifies some re:Invent 2016 attendees’ questions about SAML-based federation with AWS. For more information presented in the workshop, see the full set of workshop materials, lab guides, and CloudFormation templates. If you have follow-up questions, start a new thread in the IAM forum.

– Quint