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


Decodes additional information about the authorization status of a request from an encoded message returned in response to an AWS request.

For example, if a user is not authorized to perform an action that he or she has requested, the request returns a Client.UnauthorizedOperation response (an HTTP 403 response). Some AWS actions additionally return an encoded message that can provide details about this authorization failure.


Only certain AWS actions return an encoded authorization message. The documentation for an individual action indicates whether that action returns an encoded message in addition to returning an HTTP code.

The message is encoded because the details of the authorization status can constitute privileged information that the user who requested the action should not see. To decode an authorization status message, a user must be granted permissions via an IAM policy to request the DecodeAuthorizationMessage (sts:DecodeAuthorizationMessage) action.

The decoded message includes the following type of information:

  • Whether the request was denied due to an explicit deny or due to the absence of an explicit allow. For more information, see Determining Whether a Request is Allowed or Denied in Using IAM.
  • The principal who made the request.
  • The requested action.
  • The requested resource.
  • The values of condition keys in the context of the user's request.

Request Parameters

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


The encoded message that was returned with the response.

Type: String

Length constraints: Minimum length of 1. Maximum length of 10240.

Required: Yes

Response Elements

The following element is returned.


An XML document that contains the decoded message. For more information, see DecodeAuthorizationMessage.

Type: String


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


The error returned if the message passed to DecodeAuthorizationMessage was invalid. This can happen if the token contains invalid characters, such as linebreaks.

HTTP Status Code: 400


Sample Request

Content-Type: application/x-www-form-urlencoded; charset=utf-8
Content-Length: 1148
Expect: 100-continue
Connection: Keep-Alive

Sample Response

<?xml version="1.0" encoding="UTF-8"?>
<DecodeAuthorizationMessageResponse xmlns=""> 
      "allowed": "false",
      "explicitDeny": "false",
      "matchedStatements": "",
      "failures": "",
      "context": {
        "principal": {
          "id": "AIDACKCEVSQ6C2EXAMPLE",
          "name": "Bob",
          "arn": "arn:aws:iam::123456789012:user/Bob"
        "action": "ec2:StopInstances",
        "resource": "arn:aws:ec2:us-east-1:123456789012:instance/i-dd01c9bd",
        "conditions": [
            "item": {
              "key": "ec2:Tenancy",
              "values": ["default"]
            "item": {
              "key": "ec2:ResourceTag/elasticbeanstalk:environment-name",
              "values": ["Default-Environment"]
          (Additional items ...)