# Tag
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You can pass custom key-value pair attributes when you assume a role or federate a user. These are called session tags. You can then use the session tags to control access to resources. For more information, see [Tagging AWS STS Sessions](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_session-tags.html) in the *IAM User Guide*.

## Contents
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 ** Key **   
The key for a session tag.  
You can pass up to 50 session tags. The plain text session tag keys can’t exceed 128 characters. For these and additional limits, see [IAM and AWS STS Character Limits](https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_iam-limits.html#reference_iam-limits-entity-length) in the *IAM User Guide*.  
Type: String  
Length Constraints: Minimum length of 1. Maximum length of 128.  
Pattern: `[\p{L}\p{Z}\p{N}_.:/=+\-@]+`   
Required: Yes

 ** Value **   
The value for a session tag.  
You can pass up to 50 session tags. The plain text session tag values can’t exceed 256 characters. For these and additional limits, see [IAM and AWS STS Character Limits](https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_iam-limits.html#reference_iam-limits-entity-length) in the *IAM User Guide*.  
Type: String  
Length Constraints: Minimum length of 0. Maximum length of 256.  
Pattern: `[\p{L}\p{Z}\p{N}_.:/=+\-@]*`   
Required: Yes

## See Also
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For more information about using this API in one of the language-specific AWS SDKs, see the following:
+  [AWS SDK for C\$1\$1](https://docs.aws.amazon.com/goto/SdkForCpp/sts-2011-06-15/Tag) 
+  [AWS SDK for Java V2](https://docs.aws.amazon.com/goto/SdkForJavaV2/sts-2011-06-15/Tag) 
+  [AWS SDK for Ruby V3](https://docs.aws.amazon.com/goto/SdkForRubyV3/sts-2011-06-15/Tag)