AWS SDK Version 3 for .NET
API Reference

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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.


For PCL and Unity this operation is only available in asynchronous form. Please refer to AssumeRoleAsync.

Namespace: Amazon.SecurityToken
Assembly: AWSSDK.SecurityToken.dll
Version: 3.x.y.z


public virtual AssumeRoleResponse AssumeRole(
         AssumeRoleRequest request
Type: Amazon.SecurityToken.Model.AssumeRoleRequest

Container for the necessary parameters to execute the AssumeRole service method.

Return Value
The response from the AssumeRole service method, as returned by SecurityTokenService.


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


To assume a role

var response = client.AssumeRole(new AssumeRoleRequest 
    DurationSeconds = 3600,
    ExternalId = "123ABC",
    Policy = "{\"Version\":\"2012-10-17\",\"Statement\":[{\"Sid\":\"Stmt1\",\"Effect\":\"Allow\",\"Action\":\"s3:*\",\"Resource\":\"*\"}]}",
    RoleArn = "arn:aws:iam::123456789012:role/demo",
    RoleSessionName = "Bob"

AssumedRoleUser assumedRoleUser = response.AssumedRoleUser;
Credentials credentials = response.Credentials;
integer packedPolicySize = response.PackedPolicySize;


Version Information

.NET Framework:
Supported in: 4.5, 4.0, 3.5

Portable Class Library:
Supported in: Windows Store Apps
Supported in: Windows Phone 8.1
Supported in: Xamarin Android
Supported in: Xamarin iOS (Unified)
Supported in: Xamarin.Forms

Supported Versions: 4.6 and above
Supported Platforms: Android, iOS, Standalone

See Also