assumeRole method
Returns a set of temporary security credentials that you can use to access
AWS resources that you might not normally have access to. These temporary
credentials consist of an access key ID, a secret access key, and a
security token. Typically, you use AssumeRole within your
account or for cross-account access. For a comparison of
AssumeRole with other API operations that produce temporary
credentials, see Requesting
Temporary Security Credentials and Comparing
the AWS STS API operations in the IAM User Guide.
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. 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 in the IAM User Guide.
Session Duration
By default, the temporary security credentials created by
AssumeRole last for one hour. However, you can use the
optional DurationSeconds parameter to specify the duration of
your session. You can provide a value from 900 seconds (15 minutes) up to
the maximum session duration setting for the role. This setting can have a
value from 1 hour to 12 hours. To learn how to view the maximum value for
your role, see View
the Maximum Session Duration Setting for a Role in the IAM User
Guide. The maximum session duration limit applies when you use the
AssumeRole* API operations or the assume-role*
CLI commands. However the limit does not apply when you use those
operations to create a console URL. For more information, see Using
IAM Roles in the IAM User Guide.
Permissions
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 AWS STS GetFederationToken or
GetSessionToken API operations.
(Optional) You can pass inline or managed session policies to this operation. You can pass a single JSON policy document to use as an inline session policy. You can also specify up to 10 managed policies to use as managed session policies. The plain text that you use for both inline and managed session policies can't exceed 2,048 characters. Passing policies to this operation returns new temporary credentials. The resulting session's permissions are the intersection of the role's identity-based policy and the session policies. You can use the role's temporary credentials in subsequent AWS API calls to access resources in the account that owns the role. You cannot use session policies to grant more permissions than those allowed by the identity-based policy of the role that is being assumed. For more information, see Session Policies in the IAM User Guide.
To assume a role from a different account, 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 that access to users in the account.
A user who wants to access a role in a different account must also have
permissions that are delegated from the user account administrator. The
administrator must attach a policy that allows the user to call
AssumeRole for the ARN of the role in the other account. If
the user is in the same account as the role, then you can do either of the
following:
- Attach a policy to the user (identical to the previous user in a different account).
- Add the user as a principal directly in the role's trust policy.
Tags
(Optional) You can pass tag key-value pairs to your session. These tags are called session tags. For more information about session tags, see Passing Session Tags in STS in the IAM User Guide.
An administrator must grant you the permissions necessary to pass session tags. The administrator can also create granular permissions to allow you to pass only specific session tags. For more information, see Tutorial: Using Tags for Attribute-Based Access Control in the IAM User Guide.
You can set the session tags as transitive. Transitive tags persist during role chaining. For more information, see Chaining Roles with Session Tags in the IAM User Guide.
Using MFA with AssumeRole
(Optional) You can include multi-factor authentication (MFA) information
when you call AssumeRole. This is useful for cross-account
scenarios to ensure that the user that assumes the role has been
authenticated with 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 device produces.
May throw MalformedPolicyDocumentException. May throw PackedPolicyTooLargeException. May throw RegionDisabledException. May throw ExpiredTokenException.
Parameter roleArn :
The Amazon Resource Name (ARN) of the role to assume.
Parameter 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 that use the temporary security credentials will expose the role session name to the external account in their AWS CloudTrail logs.
The regex used to validate this parameter is a string of characters consisting of upper- and lower-case alphanumeric characters with no spaces. You can also include underscores or any of the following characters: =,.@-
Parameter durationSeconds :
The duration, in seconds, of the role session. The value can range from
900 seconds (15 minutes) up to the maximum session duration setting for
the role. This setting can have a value from 1 hour to 12 hours. If you
specify a value higher than this setting, the operation fails. For
example, if you specify a session duration of 12 hours, but your
administrator set the maximum session duration to 6 hours, your operation
fails. To learn how to view the maximum value for your role, see View
the Maximum Session Duration Setting for a Role in the IAM User
Guide.
By default, the value is set to 3600 seconds.
Parameter externalId :
A unique identifier that might be required when you assume a role in
another account. If the administrator of the account to which the role
belongs provided you with an external ID, then provide that value in the
ExternalId parameter. This value can be any string, such as a
passphrase or account number. A cross-account role is usually set up to
trust everyone in an account. Therefore, the administrator of the trusting
account might send an external ID to the administrator of the trusted
account. That way, only someone with the ID can assume the role, rather
than everyone in the account. 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 regex used to validate this parameter is a string of characters consisting of upper- and lower-case alphanumeric characters with no spaces. You can also include underscores or any of the following characters: =,.@:/-
Parameter policy :
An IAM policy in JSON format that you want to use as an inline session
policy.
This parameter is optional. Passing policies to this operation returns new temporary credentials. The resulting session's permissions are the intersection of the role's identity-based policy and the session policies. You can use the role's temporary credentials in subsequent AWS API calls to access resources in the account that owns the role. You cannot use session policies to grant more permissions than those allowed by the identity-based policy of the role that is being assumed. For more information, see Session Policies in the IAM User Guide.
The plain text that you use for both inline and managed session policies can't exceed 2,048 characters. The JSON policy characters can be any ASCII character from the space character to the end of the valid character list (\u0020 through \u00FF). It can also include the tab (\u0009), linefeed (\u000A), and carriage return (\u000D) characters.
Parameter policyArns :
The Amazon Resource Names (ARNs) of the IAM managed policies that you want
to use as managed session policies. The policies must exist in the same
account as the role.
This parameter is optional. You can provide up to 10 managed policy ARNs. However, the plain text that you use for both inline and managed session policies can't exceed 2,048 characters. For more information about ARNs, see Amazon Resource Names (ARNs) and AWS Service Namespaces in the AWS General Reference. Passing policies to this operation returns new temporary credentials. The resulting session's permissions are the intersection of the role's identity-based policy and the session policies. You can use the role's temporary credentials in subsequent AWS API calls to access resources in the account that owns the role. You cannot use session policies to grant more permissions than those allowed by the identity-based policy of the role that is being assumed. For more information, see Session Policies in the IAM User Guide.
Parameter 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 regex used to validate this parameter is a string of characters consisting of upper- and lower-case alphanumeric characters with no spaces. You can also include underscores or any of the following characters: =,.@-
Parameter tags :
A list of session tags that you want to pass. Each session tag consists of
a key name and an associated value. For more information about session
tags, see Tagging
AWS STS Sessions in the IAM User Guide.
This parameter is optional. You can pass up to 50 session tags. The plain text session tag keys can’t exceed 128 characters, and the values can’t exceed 256 characters. For these and additional limits, see IAM and STS Character Limits in the IAM User Guide. You can pass a session tag with the same key as a tag that is already attached to the role. When you do, session tags override a role tag with the same key.
Tag key–value pairs are not case sensitive, but case is preserved. This
means that you cannot have separate Department and
department tag keys. Assume that the role has the
Department=Marketing tag and you pass the
department=engineering session tag.
Department and department are not saved as
separate tags, and the session tag passed in the request takes precedence
over the role tag.
Additionally, if you used temporary credentials to perform this operation, the new session inherits any transitive session tags from the calling session. If you pass a session tag with the same key as an inherited tag, the operation fails. To view the inherited tags for a session, see the AWS CloudTrail logs. For more information, see Viewing Session Tags in CloudTrail in the IAM User Guide.
Parameter 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.
Parameter transitiveTagKeys :
A list of keys for session tags that you want to set as transitive. If you
set a tag key as transitive, the corresponding key and value passes to
subsequent sessions in a role chain. For more information, see Chaining
Roles with Session Tags in the IAM User Guide.
This parameter is optional. When you set session tags as transitive, the session policy and session tags packed binary limit is not affected.
If you choose not to specify a transitive tag key, then no tags are passed from this session to any subsequent sessions.
Implementation
Future<AssumeRoleResponse> assumeRole({
required String roleArn,
required String roleSessionName,
int? durationSeconds,
String? externalId,
String? policy,
List<PolicyDescriptorType>? policyArns,
String? serialNumber,
List<Tag>? tags,
String? tokenCode,
List<String>? transitiveTagKeys,
}) async {
ArgumentError.checkNotNull(roleArn, 'roleArn');
_s.validateStringLength(
'roleArn',
roleArn,
20,
2048,
isRequired: true,
);
ArgumentError.checkNotNull(roleSessionName, 'roleSessionName');
_s.validateStringLength(
'roleSessionName',
roleSessionName,
2,
64,
isRequired: true,
);
_s.validateNumRange(
'durationSeconds',
durationSeconds,
900,
43200,
);
_s.validateStringLength(
'externalId',
externalId,
2,
1224,
);
_s.validateStringLength(
'policy',
policy,
1,
2048,
);
_s.validateStringLength(
'serialNumber',
serialNumber,
9,
256,
);
_s.validateStringLength(
'tokenCode',
tokenCode,
6,
6,
);
final $request = <String, dynamic>{};
$request['RoleArn'] = roleArn;
$request['RoleSessionName'] = roleSessionName;
durationSeconds?.also((arg) => $request['DurationSeconds'] = arg);
externalId?.also((arg) => $request['ExternalId'] = arg);
policy?.also((arg) => $request['Policy'] = arg);
policyArns?.also((arg) => $request['PolicyArns'] = arg);
serialNumber?.also((arg) => $request['SerialNumber'] = arg);
tags?.also((arg) => $request['Tags'] = arg);
tokenCode?.also((arg) => $request['TokenCode'] = arg);
transitiveTagKeys?.also((arg) => $request['TransitiveTagKeys'] = arg);
final $result = await _protocol.send(
$request,
action: 'AssumeRole',
version: '2011-06-15',
method: 'POST',
requestUri: '/',
exceptionFnMap: _exceptionFns,
shape: shapes['AssumeRoleRequest'],
shapes: shapes,
resultWrapper: 'AssumeRoleResult',
);
return AssumeRoleResponse.fromXml($result);
}