Is it possible to send form data to API Gateway with AWS_IAM Authorizer on?

I’m curious if it is possible to send html form data to API Gateway when the aws_iam authorizer is securing the API endpoint. When AWS_IAM Authorizer is on the endpoint, the request must be signed with an AWS signature. That signature requires string values, and since I’m setting my request body to form data, I have been unable to figure out a way to sign the request and correctly pass my request to my endpoint.

Any workarounds?