Cognito Pre-Token Generation Lambda Cannot Accept List Overrides

Question

Looking at the docs for Cognito pre-token generation lambda hooks: https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-lambda-pre-token-generation.html

I see I can change the fields in the ID token. One field I need to update involves setting the value to an array: e.g. `"permissions": ["read", "write", "execute"]`.

This is what my Lambda looks like
```
exports.handler = (event, context, callback) => {
    event.response = {
        "claimsOverrideDetails": {
            "claimsToAddOrOverride": {
                "role": "user",
                "permissions": ["read", "write", "execute"]
            }
        }
    };

callback(null, event);
};
```
However, the hook fails. JWT allows for there to be array (and object) parameters. Any idea when this feature might be enabled?

Thanks!

chanster · Answer

Is there any update or plan when this feature will be implemented?
We really need this feature for an amplify application where we want to make use of the "groupClaim" attribute which we want to generate by ourselves in a pre token lambda function. 
I cannot really understand why there is this option (groupClaim in graphql auth) when you cannot create another array then cognitogroups with AWS cognito pre token generation lambda.

lis10app · Answer

This bug has been around for almost 5 years now, like JaccoPK said. Is there any update or plan when this feature will be implemented? It's becoming a very big problem with Amplify/Appsync apps and with how their resolvers handle custom claims.

Mahmoud Matouk · Answer

Hi,

Currently only string type is supported for custom claims, you need to represent your list as a string. something like that...
"permissions": "[read, write, execute]"

Cognito Pre-Token Generation Lambda Cannot Accept List Overrides

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