AWS Identity and Access Management
User Guide

Creating a Role to Delegate Permissions to an IAM User

You can use IAM roles to delegate access to your AWS resources. With IAM roles, you can establish trust relationships between your trusting account and other AWS trusted accounts. The trusting account owns the resource to be accessed and the trusted account contains the users who need access to the resource. However, it is possible for another account to own a resource in your account. For example, the trusting account might allow the trusted account to create new resources, such as creating new objects in an Amazon S3 bucket. In that case, the account that creates the resource owns the resource and controls who can access that resource.

After you create the trust relationship, an IAM user or an application from the trusted account can use the AWS Security Token Service (AWS STS) AssumeRole API operation. This operation provides temporary security credentials that enable access to AWS resources in your account.

The accounts can both be controlled by you, or the account with the users can be controlled by a third party. If the other account with the users is in an AWS account that you do not control, then you can use the externalId attribute. The external ID can be any word or number that is agreed upon between you and the administrator of the third-party account. This option automatically adds a condition to the trust policy that allows the user to assume the role only if the request includes the correct sts:ExternalID. For more information, see How to Use an External ID When Granting Access to Your AWS Resources to a Third Party.

For information about how to use roles to delegate permissions, see Roles Terms and Concepts. For information about using a service role to allow services to access resources in your account, see Creating a Role to Delegate Permissions to an AWS Service.

Creating an IAM Role (Console)

You can use the AWS Management Console to create a role that an IAM user can assume. For example, assume that your organization has multiple AWS accounts to isolate a development environment from a production environment. For a high-level description of the steps to set up and use a role that allows users in the development account to access resources in the production account, see Example Scenario Using Separate Development and Production Accounts.

To create a role (console)

  1. Sign in to the AWS Management Console and open the IAM console at https://console.aws.amazon.com/iam/.

  2. In the navigation pane of the console, choose Roles and then choose Create role.

  3. Choose the Another AWS account role type.

  4. For Account ID, type the AWS account ID to which you want to grant access to your resources.

    The administrator of the specified account can grant permission to assume this role to any IAM user in that account. To do this, the administrator attaches a policy to the user or a group that grants permission for the sts:AssumeRole action. That policy must specify the role's ARN as the Resource.

  5. If you are granting permissions to users from an account that you do not control, and the users will assume this role programmatically, then select Require external ID. The external ID can be any word or number that is agreed upon between you and the administrator of the third-party account. This option automatically adds a condition to the trust policy that allows the user to assume the role only if the request includes the correct sts:ExternalID. For more information, see How to Use an External ID When Granting Access to Your AWS Resources to a Third Party.

    Important

    Choosing this option restricts access to the role only through the AWS CLI, Tools for Windows PowerShell, or the AWS API. This is because you cannot use the AWS console to switch to a role that has an externalId condition in its trust policy. However, you can create this kind of access programmatically by writing a script or an application using the relevant SDK. For more information and a sample script, see How to Enable Cross-Account Access to the AWS Management Console in the AWS Security Blog.

  6. If you want to restrict the role to users who sign in with multi-factor authentication (MFA), select Require MFA. This adds a condition to the role's trust policy that checks for an MFA sign-in. A user who wants to assume the role must sign in with a temporary one-time password from a configured MFA device. Users without MFA authentication cannot assume the role. For more information about MFA, see Using Multi-Factor Authentication (MFA) in AWS

  7. Choose Next: Permissions.

  8. IAM includes a list of the AWS managed and customer managed policies in your account. Select the policy to use for the permissions policy or choose Create policy to open a new browser tab and create a new policy from scratch. For more information, see step 4 in the procedure Creating IAM Policies (Console). After you create the policy, close that tab and return to your original tab. Select the check box next to the permissions policies that you want anyone who assumes the role to have. If you prefer, you can select no policies at this time, and then attach policies to the role later. By default, a role has no permissions.

  9. (Optional) Set a permissions boundary. This is an advanced feature.

    Open the Set permissions boundary section and choose Use a permissions boundary to control the maximum role permissions. Select the policy to use for the permissions boundary.

  10. Choose Next: Tagging.

  11. (Optional) Add metadata to the role by attaching tags as key–value pairs. For more information about using tags in IAM, see Tagging IAM Identities.

  12. Choose Next: Review.

  13. For Role name, type a name for your role. Role names must be unique within your AWS account. They are not distinguished by case. For example, you cannot create roles named both PRODROLE and prodrole. Because other AWS resources might reference the role, you cannot edit the name of the role after it has been created.

  14. (Optional) For Role description, type a description for the new role.

  15. Review the role and then choose Create role.

    Important

    Remember that this is only the first half of the configuration required. You must also give individual users in the trusted account permissions to switch to the role in the console, or assume the role programmatically. For more information about this step, see Granting a User Permissions to Switch Roles.

Creating an IAM Role (AWS CLI)

Creating a role from the AWS CLI involves multiple steps. When you use the console to create a role, many of the steps are done for you, but with the AWS CLI you must explicitly perform each step yourself. You must create the role and then assign a permissions policy to the role. Optionally, you can also set the permissions boundary for your role.

To create a role for cross-account access (AWS CLI)

  1. Create a role: aws iam create-role

  2. Attach a managed permissions policy to the role: aws iam attach-role-policy

    or

    Create an inline permissions policy for the role: aws iam put-role-policy

  3. (Optional) Add custom attributes to the role by attaching tags: aws iam tag-role

    For more information, see Managing Tags on IAM Identities (AWS CLI or AWS API).

  4. (Optional) Set the permissions boundary for the role: aws iam put-role-permissions-boundary

    A permissions boundary controls the maximum permissions that a role can have. Permissions boundaries are an advanced AWS feature.

The following example shows the first two, and most common steps for creating a cross-account role in a simple environment. This example allows any user in the 123456789012 account to assume the role and view the example_bucket Amazon S3 bucket. This example also assumes that you are using a client computer running Windows, and have already configured your command line interface with your account credentials and region. For more information, see Configuring the AWS Command Line Interface.

In this example, include the following trust policy in the first command when you create the role. This trust policy allows users in the 123456789012 account to assume the role using the AssumeRole operation, but only if the user provides MFA authentication using the SerialNumber and TokenCode parameters. For more information about MFA, see Using Multi-Factor Authentication (MFA) in AWS.

{ "Version": "2012-10-17", "Statement": { "Effect": "Allow", "Principal": { "AWS": "arn:aws:iam::123456789012:root" }, "Action": "sts:AssumeRole", "Condition": { "Bool": { "aws:MultiFactorAuthPresent": "true" } } } }

Important

If your Principal element contains the ARN for a specific IAM role or user, then that ARN is transformed to a unique principal ID when the policy is saved. This helps mitigate the risk of someone escalating their permissions by removing and recreating the role or user. You don't normally see this ID in the console because there is also a reverse transformation back to the ARN when the trust policy is displayed. However, if you delete the role or user, then the principal ID appears in the console because AWS can no longer map it back to an ARN. Therefore, if you delete and recreate a user or role referenced in a trust policy's Principal element, you must edit the role to replace the ARN.

When you use the second command, you must attach an existing managed policy to the role. The following permissions policy allows anyone who assumes the role to perform only the ListBucket action on the example_bucket Amazon S3 bucket.

{ "Version": "2012-10-17", "Statement": { "Effect": "Allow", "Action": "s3:ListBucket", "Resource": "arn:aws:s3:::example_bucket" } }

To create this Test-UserAccess-Role role, you must first save the previous trust policy with the name trustpolicyforacct123456789012.json to the policies folder in your local C: drive. Then save the previous permissions policy as a customer managed policy in your AWS account with the name PolicyForRole. You can then use the following commands to create the role and attach the managed policy.

# Create the role and attach the trust policy file that allows users in the specified account to assume the role. $ aws iam create-role --role-name Test-UserAccess-Role --assume-role-policy-document file://C:\policies\trustpolicyforacct123456789012.json # Attach the permissions policy (in this example a managed policy) to the role to specify what it is allowed to do. $ aws iam attach-role-policy --role-name Test-UserAccess-Role --policy-arn arn:aws:iam::123456789012:role/PolicyForRole

Important

Remember that this is only the first half of the configuration required. You must also give individual users in the trusted account permissions to switch to the role. For more information about this step, see Granting a User Permissions to Switch Roles.

After you create the role and grant it permissions to perform AWS tasks or access AWS resources, any users in the 123456789012 account can assume the role. For more information, see Switching to an IAM Role (AWS CLI).

Creating an IAM Role (AWS API)

Creating a role from the AWS API involves multiple steps. When you use the console to create a role, many of the steps are done for you, but with the API you must explicitly perform each step yourself. You must create the role and then assign a permissions policy to the role. Optionally, you can also set the permissions boundary for your role.

To create a role in code (AWS API)

  1. Create a role: CreateRole

    For the role's trust policy, you can specify a file location.

  2. Attach a managed permission policy to the role: AttachRolePolicy

    or

    Create an inline permission policy for the role: PutRolePolicy

    Important

    Remember that this is only the first half of the configuration required. You must also give individual users in the trusted account permissions to switch to the role. For more information about this step, see Granting a User Permissions to Switch Roles.

  3. (Optional) Add custom attributes to the user by attaching tags: TagRole

    For more information, see Managing Tags on IAM Identities (AWS CLI or AWS API).

  4. (Optional) Set the permissions boundary for the role: PutRolePermissionsBoundary

    A permissions boundary controls the maximum permissions that a role can have. Permissions boundaries are an advanced AWS feature.

After you create the role and grant it permissions to perform AWS tasks or access AWS resources, you must grant permissions to users in the account to allow them to assume the role. For more information about assuming a role, see Switching to an IAM Role (AWS API).