Combine Sub and Ref function

Question

I have the following Principal ARN but I am getting error ""Policy contains a statement with one or more invalid principals". Is it possible to combine sub and ref function?

```
            Principal:
               AWS:
                  - !Sub arn:aws:iam::${AWS::AccountId}:role/aws-reserved/sso.amazonaws.com/${AWS::Region}/!Ref AssumedRole 
              Action: '*'
              Resource: '*'
```

Accepted Answer

Yes, and actually you are already doing it but perhaps did not realise. When using !Sub the !Ref (and !GetAtt) syntax switches to using ${...} instead. So for example where you have used ${AWS::Region} is the equivalent of using !Ref AWS::Region so in your example it would be:

        Principal:
           AWS:
              - !Sub arn:aws:iam::${AWS::AccountId}:role/aws-reserved/sso.amazonaws.com/${AWS::Region}/${AssumedRole}
          Action: '*'
          Resource: '*'

I hope this makes sense.

Principal:
               AWS:
                  - !Sub arn:aws:iam::${AWS::AccountId}:role/aws-reserved/sso.amazonaws.com/${AWS::Region}/${AssumedRole}
              Action: '*'
              Resource: '*'

I hope this makes sense.

Answer

Hello.

I don't think it's necessary to combine them.  
As stated in the following document, if you specify the logical ID of !Sub as ${AssumedRole}, you can get the same value as !Ref.  
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-sub.html#w8aac34c28c69b7  
> If you specify template parameter names or resource logical IDs, such as ${InstanceTypeParameter}, CloudFormation returns the same values as if you used the Ref intrinsic function. If you specify resource attributes, such as ${MyInstance.PublicIp}, CloudFormation returns the same values as if you used the Fn::GetAtt intrinsic function.

I think the problem can be solved simply by doing the following:  
```
!Sub arn:aws:iam::${AWS::AccountId}:role/aws-reserved/sso.amazonaws.com/${AWS::Region}/${AssumedRole}
```

Combine Sub and Ref function

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