How to AWS API Gateway Service Proxy Authentication

Recently I tried to bypass Lambda and directly save object the s3 using API Gateway Service Proxy . I abled to manage that part but I’m struggle to authenticate the Rest API call from the API Gateway. Appreciate you guidance to implement authentication part.

My serverless implementation


        - s3:
            path: /s3
            method: post
            action: PutObject
            pathOverride: '{file}.xml'
            bucket: 'docusign-temp'
            cors: true
          'integration.request.path.file': 'context.requestId'
          'integration.request.path.object': 'context.requestId'
          'integration.request.header.X-DocuSign-Signature-1': "'WV/YmpqEAHgWC86WACTJiiY='"

Request Headers are mapped with the Integration Request phase but there not allowed to do the authentication part. I need to pass these header to the Method Request phase where I can do the authentication part.