Using the AWS S3 golang SDK with Google default credentials

main.go

package main

import (
        "context"
        "fmt"
        "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"
        "log"
)

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

func main() {
        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) {
                        creds, err := google.FindDefaultCredentials(context.Background(), "https://storage.googleapis.com")
                        if err != nil {
                                log.Printf("No creds: %s", err)
                        } else {
                                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)
        }
}