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Is it possible to throw custom error message from API Gateway Lambda Authorizer


I have created an Lambda Authorizer for custom authorization in API Gateway. I need to throw custom error message like this.

{ errorCode: 'xyz_12#', errorType: 'Constraint error', errorMessage: 'Need permission to perform this action', statusCode: 401 }

Is it possible from lambda authorizer?

1 Answer

Yes. At the end of the example authorizer in the docs (, there is way to output optional data. Updating with your values, it would be something like this:

    // Optional output with custom properties of the String, Number or Boolean type.
    authResponse.context = {
        "errorCode": "xyz_12#",
        "errorType": "Constraint error",
        "errorMessage": "Need permisssion to perform this action"

In the body mapping template, you'd access these as follows:

{"errorCode":"$context.authorizer.context.errorCode", "errorType": "$context.authorizer.context.errorCode"}

The one caveat here is that you can't specify the HTTP error code. The authorizer has to generate a 'Deny' policy which then results in an HTTP 403.

More discussion is available here:

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answered 5 months ago

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