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AWS Security Token Service
API Reference (API Version 2011-06-15)

AssumeRole

Returns a set of temporary security credentials (consisting of an access key ID, a secret access key, and a security token) that you can use to access AWS resources that you might not normally have access to. Typically, you use AssumeRole for cross-account access or federation. For a comparison of AssumeRole with the other APIs that produce temporary credentials, see Requesting Temporary Security Credentials and Comparing the AWS STS APIs in the IAM User Guide.

Important: You cannot call AssumeRole by using AWS root account credentials; access is denied. You must use credentials for an IAM user or an IAM role to call AssumeRole.

For cross-account access, imagine that you own multiple accounts and need to access resources in each account. You could create long-term credentials in each account to access those resources. However, managing all those credentials and remembering which one can access which account can be time consuming. Instead, you can create one set of long-term credentials in one account and then use temporary security credentials to access all the other accounts by assuming roles in those accounts. For more information about roles, see IAM Roles (Delegation and Federation) in the IAM User Guide.

For federation, you can, for example, grant single sign-on access to the AWS Management Console. If you already have an identity and authentication system in your corporate network, you don't have to recreate user identities in AWS in order to grant those user identities access to AWS. Instead, after a user has been authenticated, you call AssumeRole (and specify the role with the appropriate permissions) to get temporary security credentials for that user. With those temporary security credentials, you construct a sign-in URL that users can use to access the console. For more information, see Common Scenarios for Temporary Credentials in the IAM User Guide.

The temporary security credentials are valid for the duration that you specified when calling AssumeRole, which can be from 900 seconds (15 minutes) to a maximum of 3600 seconds (1 hour). The default is 1 hour.

The temporary security credentials created by AssumeRole can be used to make API calls to any AWS service with the following exception: you cannot call the STS service's GetFederationToken or GetSessionToken APIs.

Optionally, you can pass an IAM access policy to this operation. If you choose not to pass a policy, the temporary security credentials that are returned by the operation have the permissions that are defined in the access policy of the role that is being assumed. If you pass a policy to this operation, the temporary security credentials that are returned by the operation have the permissions that are allowed by both the access policy of the role that is being assumed, and the policy that you pass. This gives you a way to further restrict the permissions for the resulting temporary security credentials. You cannot use the passed policy to grant permissions that are in excess of those allowed by the access policy of the role that is being assumed. For more information, see Permissions for AssumeRole, AssumeRoleWithSAML, and AssumeRoleWithWebIdentity in the IAM User Guide.

To assume a role, your AWS account must be trusted by the role. The trust relationship is defined in the role's trust policy when the role is created. That trust policy states which accounts are allowed to delegate access to this account's role.

The user who wants to access the role must also have permissions delegated from the role's administrator. If the user is in a different account than the role, then the user's administrator must attach a policy that allows the user to call AssumeRole on the ARN of the role in the other account. If the user is in the same account as the role, then you can either attach a policy to the user (identical to the previous different account user), or you can add the user as a principal directly in the role's trust policy

Using MFA with AssumeRole

You can optionally include multi-factor authentication (MFA) information when you call AssumeRole. This is useful for cross-account scenarios in which you want to make sure that the user who is assuming the role has been authenticated using an AWS MFA device. In that scenario, the trust policy of the role being assumed includes a condition that tests for MFA authentication; if the caller does not include valid MFA information, the request to assume the role is denied. The condition in a trust policy that tests for MFA authentication might look like the following example.

"Condition": {"Bool": {"aws:MultiFactorAuthPresent": true}}

For more information, see Configuring MFA-Protected API Access in the IAM User Guide guide.

To use MFA with AssumeRole, you pass values for the SerialNumber and TokenCode parameters. The SerialNumber value identifies the user's hardware or virtual MFA device. The TokenCode is the time-based one-time password (TOTP) that the MFA devices produces.

Request Parameters

For information about the parameters that are common to all actions, see Common Parameters.

DurationSeconds

The duration, in seconds, of the role session. The value can range from 900 seconds (15 minutes) to 3600 seconds (1 hour). By default, the value is set to 3600 seconds.

Type: Integer

Valid Range: Minimum value of 900. Maximum value of 3600.

Required: No

ExternalId

A unique identifier that is used by third parties when assuming roles in their customers' accounts. For each role that the third party can assume, they should instruct their customers to ensure the role's trust policy checks for the external ID that the third party generated. Each time the third party assumes the role, they should pass the customer's external ID. The external ID is useful in order to help third parties bind a role to the customer who created it. For more information about the external ID, see How to Use an External ID When Granting Access to Your AWS Resources to a Third Party in the IAM User Guide.

The format for this parameter, as described by its regex pattern, is a string of characters consisting of upper- and lower-case alphanumeric characters with no spaces. You can also include any of the following characters: =,.@:\/-

Type: String

Length Constraints: Minimum length of 2. Maximum length of 1224.

Pattern: [\w+=,.@:\/-]*

Required: No

Policy

An IAM policy in JSON format.

This parameter is optional. If you pass a policy, the temporary security credentials that are returned by the operation have the permissions that are allowed by both (the intersection of) the access policy of the role that is being assumed, and the policy that you pass. This gives you a way to further restrict the permissions for the resulting temporary security credentials. You cannot use the passed policy to grant permissions that are in excess of those allowed by the access policy of the role that is being assumed. For more information, see Permissions for AssumeRole, AssumeRoleWithSAML, and AssumeRoleWithWebIdentity in the IAM User Guide.

The format for this parameter, as described by its regex pattern, is a string of characters up to 2048 characters in length. The characters can be any ASCII character from the space character to the end of the valid character list (\u0020-\u00FF). It can also include the tab (\u0009), linefeed (\u000A), and carriage return (\u000D) characters.

Note

The policy plain text must be 2048 bytes or shorter. However, an internal conversion compresses it into a packed binary format with a separate limit. The PackedPolicySize response element indicates by percentage how close to the upper size limit the policy is, with 100% equaling the maximum allowed size.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 2048.

Pattern: [\u0009\u000A\u000D\u0020-\u00FF]+

Required: No

RoleArn

The Amazon Resource Name (ARN) of the role to assume.

Type: String

Length Constraints: Minimum length of 20. Maximum length of 2048.

Pattern: [\u0009\u000A\u000D\u0020-\u007E\u0085\u00A0-\uD7FF\uE000-\uFFFD\u10000-\u10FFFF]+

Required: Yes

RoleSessionName

An identifier for the assumed role session.

Use the role session name to uniquely identify a session when the same role is assumed by different principals or for different reasons. In cross-account scenarios, the role session name is visible to, and can be logged by the account that owns the role. The role session name is also used in the ARN of the assumed role principal. This means that subsequent cross-account API requests using the temporary security credentials will expose the role session name to the external account in their CloudTrail logs.

The format for this parameter, as described by its regex pattern, is a string of characters consisting of upper- and lower-case alphanumeric characters with no spaces. You can also include any of the following characters: =,.@-

Type: String

Length Constraints: Minimum length of 2. Maximum length of 64.

Pattern: [\w+=,.@-]*

Required: Yes

SerialNumber

The identification number of the MFA device that is associated with the user who is making the AssumeRole call. Specify this value if the trust policy of the role being assumed includes a condition that requires MFA authentication. The value is either the serial number for a hardware device (such as GAHT12345678) or an Amazon Resource Name (ARN) for a virtual device (such as arn:aws:iam::123456789012:mfa/user).

The format for this parameter, as described by its regex pattern, is a string of characters consisting of upper- and lower-case alphanumeric characters with no spaces. You can also include any of the following characters: =,.@-

Type: String

Length Constraints: Minimum length of 9. Maximum length of 256.

Pattern: [\w+=/:,.@-]*

Required: No

TokenCode

The value provided by the MFA device, if the trust policy of the role being assumed requires MFA (that is, if the policy includes a condition that tests for MFA). If the role being assumed requires MFA and if the TokenCode value is missing or expired, the AssumeRole call returns an "access denied" error.

The format for this parameter, as described by its regex pattern, is a sequence of six numeric digits.

Type: String

Length Constraints: Fixed length of 6.

Pattern: [\d]*

Required: No

Response Elements

The following elements are returned by the service.

AssumedRoleUser

The Amazon Resource Name (ARN) and the assumed role ID, which are identifiers that you can use to refer to the resulting temporary security credentials. For example, you can reference these credentials as a principal in a resource-based policy by using the ARN or assumed role ID. The ARN and ID include the RoleSessionName that you specified when you called AssumeRole.

Type: AssumedRoleUser object

Credentials

The temporary security credentials, which include an access key ID, a secret access key, and a security (or session) token.

Note: The size of the security token that STS APIs return is not fixed. We strongly recommend that you make no assumptions about the maximum size. As of this writing, the typical size is less than 4096 bytes, but that can vary. Also, future updates to AWS might require larger sizes.

Type: Credentials object

PackedPolicySize

A percentage value that indicates the size of the policy in packed form. The service rejects any policy with a packed size greater than 100 percent, which means the policy exceeded the allowed space.

Type: Integer

Valid Range: Minimum value of 0.

Errors

For information about the errors that are common to all actions, see Common Errors.

MalformedPolicyDocument

The request was rejected because the policy document was malformed. The error message describes the specific error.

HTTP Status Code: 400

PackedPolicyTooLarge

The request was rejected because the policy document was too large. The error message describes how big the policy document is, in packed form, as a percentage of what the API allows.

HTTP Status Code: 400

RegionDisabled

STS is not activated in the requested region for the account that is being asked to generate credentials. The account administrator must use the IAM console to activate STS in that region. For more information, see Activating and Deactivating AWS STS in an AWS Region in the IAM User Guide.

HTTP Status Code: 403

Example

Sample Request

https://sts.amazonaws.com/
?Version=2011-06-15
&Action=AssumeRole
&RoleSessionName=Bob
&RoleArn=arn:aws:iam::123456789012:role/demo
&Policy={"Version":"2012-10-17","Statement":[{"Sid":"Stmt1",
"Effect":"Allow","Action":"s3:*","Resource":"*"}]}
&DurationSeconds=3600
&ExternalId=123ABC
&AUTHPARAMS

Sample Response

<AssumeRoleResponse xmlns="https://sts.amazonaws.com/doc/
2011-06-15/">
  <AssumeRoleResult>
    <Credentials>
      <SessionToken>
       AQoDYXdzEPT//////////wEXAMPLEtc764bNrC9SAPBSM22wDOk4x4HIZ8j4FZTwdQW
       LWsKWHGBuFqwAeMicRXmxfpSPfIeoIYRqTflfKD8YUuwthAx7mSEI/qkPpKPi/kMcGd
       QrmGdeehM4IC1NtBmUpp2wUE8phUZampKsburEDy0KPkyQDYwT7WZ0wq5VSXDvp75YU
       9HFvlRd8Tx6q6fE8YQcHNVXAkiY9q6d+xo0rKwT38xVqr7ZD0u0iPPkUL64lIZbqBAz
       +scqKmlzm8FDrypNC9Yjc8fPOLn9FX9KSYvKTr4rvx3iSIlTJabIQwj2ICCR/oLxBA==
      </SessionToken>
      <SecretAccessKey>
       wJalrXUtnFEMI/K7MDENG/bPxRfiCYzEXAMPLEKEY
      </SecretAccessKey>
      <Expiration>2011-07-15T23:28:33.359Z</Expiration>
      <AccessKeyId>AKIAIOSFODNN7EXAMPLE</AccessKeyId>
    </Credentials>
    <AssumedRoleUser>
      <Arn>arn:aws:sts::123456789012:assumed-role/demo/Bob</Arn>
      <AssumedRoleId>ARO123EXAMPLE123:Bob</AssumedRoleId>
    </AssumedRoleUser>
    <PackedPolicySize>6</PackedPolicySize>
  </AssumeRoleResult>
  <ResponseMetadata>
    <RequestId>c6104cbe-af31-11e0-8154-cbc7ccf896c7</RequestId>
  </ResponseMetadata>
</AssumeRoleResponse>