Golang to access the AWS metadata endpoint

aws_metadata_endpoint.go

package main

import (
        "encoding/json"
        "fmt"
        "io"
        "net/http"
        "os"
)

// You could add more fields here. The JSON looks like:
/*
{
  "Code" : "Success",
  "LastUpdated" : "2023-08-14T16:29:41Z",
  "Type" : "AWS-HMAC",
  "AccessKeyId" : "ASDF1234",
  "SecretAccessKey" : "SUPERSECRET",
  "Token" : "blahdiblah",
  "Expiration" : "2023-08-14T22:56:15Z"
}
*/
type credentialsResponse struct {
        Code string
        Token string
}

func main() {
        metadataUrl := "http://169.254.169.254"

        metadataToken := getMetadataToken(metadataUrl)
        //fmt.Printf("metadata token: %s\n", string(metadataToken))
        credsToken := getCredsToken(metadataUrl, metadataToken)
        //fmt.Printf("creds token: %s\n", credsToken)


}

func getMetadataToken(url string) string {
        endpoint := fmt.Sprintf("%s/latest/api/token", url)

        req , err := http.NewRequest("PUT", endpoint, nil)
        req.Header.Set("X-Aws-Ec2-Metadata-Token-Ttl-Seconds", "21600")
        if err != nil {
                exitErrorf("Error creating request", err)
        }

        resp, err := http.DefaultClient.Do(req)
        if err != nil {
                exitErrorf("Error making request", err)
        }
        defer resp.Body.Close()

        token, err := io.ReadAll(resp.Body)
        if err != nil {
                exitErrorf("Error reading token body", err)
        }
        //fmt.Printf("token: %s\n", string(token))

        return string(token)
}

func getCredsToken(url string, token string) string {
        endpoint := fmt.Sprintf("%s/latest/meta-data/identity-credentials/ec2/security-credentials/ec2-instance", url)
        req, err := http.NewRequest("GET", endpoint, nil)
        if err != nil {
                exitErrorf("Error creating request", err)
        }

        req.Header.Set("X-Aws-Ec2-Metadata-Token", string(token))
        resp, err := http.DefaultClient.Do(req)
        if err != nil {
                exitErrorf("Error making request", err)
        }
        defer resp.Body.Close()

        body, err := io.ReadAll(resp.Body)
        if err != nil {
                exitErrorf("Error reading credentials body", err)
        }
        //fmt.Printf("creds body: %s\n", string(body))

        var creds credentialsResponse
        if err := json.Unmarshal(body, &creds); err != nil {   // Parse []byte to go struct pointer
                exitErrorf("Can not unmarshal creds JSON", err)
        }
        //fmt.Printf("creds: %+v\n", creds)

        return creds.Token
}

func exitErrorf(msg string, args ...interface{}) {
        fmt.Fprintf(os.Stderr, msg+"\n", args...)
        os.Exit(1)
}