Using the AWS S3 golang SDK with Google default credentials

main.go

package main

import (
	"context"
	"fmt"
	"log"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/request"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/aws/aws-sdk-go/service/s3"
	"golang.org/x/oauth2/google"
)

// This isn't production worthy code. It's just showing which libraries and entrypoints you might use to do this.

func main() {
	creds, err := google.FindDefaultCredentials(context.Background(), "https://storage.googleapis.com")
	if err != nil {
		log.Fatalf("No creds: %s", err)
	}
	s3client := s3.New(session.New(), aws.NewConfig().WithEndpoint("storage.googleapis.com").WithRegion("us-central1"))
	s3client.Handlers.Sign.Clear()
	s3client.Handlers.Sign.PushBackNamed(request.NamedHandler{
		Name: "GoogleOauth",
		Fn: func(req *request.Request) {
			token, err := creds.TokenSource.Token()
			if err != nil {
				log.Printf("No token source: %s", err)
			} else {
				authzHeaderVal := fmt.Sprintf("%s %s", token.TokenType, token.AccessToken)
				log.Printf("Signing that beast! %s", authzHeaderVal)
				req.HTTPRequest.Header.Set("Authorization", authzHeaderVal)
			}
		},
	})
	headOp := &s3.HeadObjectInput{
		Bucket: aws.String("mybucket"),
		Key:    aws.String("whatever/path"),
	}
	_, err := s3client.HeadObject(headOp)
	if err != nil {
		log.Printf("Head failed: %s", err)
	}
}