**To decode a authorization failure message**

The following ``decode-authorization-message`` example decodes the message returned by the EC2 console when attempting to launch an instance without the required permissions. ::

    aws sts decode-authorization-message \
        --encoded-message  

The output is formatted as a single-line string of JSON text that you can parse with any JSON text processor. ::

    {
        "DecodedMessage": "{\"allowed\":false,\"explicitDeny\":false,\"matchedStatements\":{\"items\":[]},\"failures\":{\"items\":[]},\"context\":{\"principal\":{\"id\":\"AIDAV3ZUEFP6J7GY7O6LO\",\"name\":\"chain-user\",\"arn\":\"arn:aws:iam::403299380220:user/chain-user\"},\"action\":\"ec2:RunInstances\",\"resource\":\"arn:aws:ec2:us-east-2:403299380220:instance/*\",\"conditions\":{\"items\":[{\"key\":\"ec2:InstanceMarketType\",\"values\":{\"items\":[{\"value\":\"on-demand\"}]}},{\"key\":\"aws:Resource\",\"values\":{\"items\":[{\"value\":\"instance/*\"}]}},{\"key\":\"aws:Account\",\"values\":{\"items\":[{\"value\":\"403299380220\"}]}},{\"key\":\"ec2:AvailabilityZone\",\"values\":{\"items\":[{\"value\":\"us-east-2b\"}]}},{\"key\":\"ec2:ebsOptimized\",\"values\":{\"items\":[{\"value\":\"false\"}]}},{\"key\":\"ec2:IsLaunchTemplateResource\",\"values\":{\"items\":[{\"value\":\"false\"}]}},{\"key\":\"ec2:InstanceType\",\"values\":{\"items\":[{\"value\":\"t2.micro\"}]}},{\"key\":\"ec2:RootDeviceType\",\"values\":{\"items\":[{\"value\":\"ebs\"}]}},{\"key\":\"aws:Region\",\"values\":{\"items\":[{\"value\":\"us-east-2\"}]}},{\"key\":\"aws:Service\",\"values\":{\"items\":[{\"value\":\"ec2\"}]}},{\"key\":\"ec2:InstanceID\",\"values\":{\"items\":[{\"value\":\"*\"}]}},{\"key\":\"aws:Type\",\"values\":{\"items\":[{\"value\":\"instance\"}]}},{\"key\":\"ec2:Tenancy\",\"values\":{\"items\":[{\"value\":\"default\"}]}},{\"key\":\"ec2:Region\",\"values\":{\"items\":[{\"value\":\"us-east-2\"}]}},{\"key\":\"aws:ARN\",\"values\":{\"items\":[{\"value\":\"arn:aws:ec2:us-east-2:403299380220:instance/*\"}]}}]}}}"
    }

For more information, see `How can I decode an authorization failure message after receiving an "UnauthorizedOperation" error during an EC2 instance launch? <https://repost.aws/knowledge-center/ec2-not-auth-launch>`__ in *AWS re:Post*.