AWS API Gateway がリクエストヘッダーを小文字にしてしまう時の解決策 (golang)

package main

import (
    "errors"
    "fmt"
    "log"

    "github.com/aws/aws-lambda-go/events"
    "github.com/aws/aws-lambda-go/lambda"
    "github.com/aws/aws-lambda-go/lambdacontext"
)

type (
    request  = events.APIGatewayProxyRequest
    response = events.APIGatewayProxyResponse
)

// handler handles AWS Lambda execution.
func handler(ctx context.Context, r request) (response, error) {
    if _, ok := lambdacontext.FromContext(ctx); !ok {
        return response{StatusCode: http.StatusBadRequest}, errors.New("not invoked from aws lambda")
    }
    log.Print(r.Headers)
    accept, _ := r.Headers["Accept"] // 実際は accept としないと取得できない
    if == strings.Contains(accept, "application/json") {
        return response{StatusCode: http.StatusOK, Body:"{}"}, nil
    }
    return response{StatusCode: http.StatusOK, Body: fmt.Sprintf("It Works! path=%s", r.Path)}, nil
}

func main() {
    lambda.Start(handler)
}

curl -X GET -H "Accept:application/json" https://hogehoge

headers := http.Header{}
for header, values := range r.MultiValueHeaders {
    for _, value := range values {
        headers.Add(header, value)
    }
}

headers.Get("Accept")