fix(auth) improve error when passing a PEM key as ServiceAccountKey (#3878)

* fix(auth) improve error when passing a PEM key as ServiceAccountKey

* fix(auth) add changelog message

* fix(auth) bump version

* fix(auth) increase patch instead of minor version

Author: cgoetz-inovex

core/CHANGELOG.md

@@ -1,3 +1,6 @@
+## v0.20.1
+- **Improvement:** Improve error message when passing a PEM encoded file to as service account key
+
 ## v0.20.0
 - **New:** Added new `GetTraceId` function
 

core/VERSION

@@ -1 +1 @@
-v0.20.0
+v0.20.1

core/auth/auth.go

@@ -6,6 +6,7 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/stackitcloud/stackit-sdk-go/core/clients"
 	"github.com/stackitcloud/stackit-sdk-go/core/config"
@@ -172,7 +173,11 @@ func KeyAuth(cfg *config.Configuration) (http.RoundTripper, error) {
 	var serviceAccountKey = &clients.ServiceAccountKeyResponse{}
 	err = json.Unmarshal([]byte(cfg.ServiceAccountKey), serviceAccountKey)
 	if err != nil {
-		return nil, fmt.Errorf("unmarshalling service account key: %w", err)
+		var errorSuffix string
+		if strings.HasPrefix(cfg.ServiceAccountKey, "-----BEGIN") {
+			errorSuffix = " - it seems like the provided service account key is in PEM format. Please provide it in JSON format."
+		}
+		return nil, fmt.Errorf("unmarshalling service account key: %w%s", err, errorSuffix)
 	}
 
 	// Try to get private key from configuration, environment or credentials file

core/auth/auth_test.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"os"
 	"reflect"
+	"strings"
 	"testing"
 	"time"
 
@@ -668,6 +669,19 @@ func TestKeyAuth(t *testing.T) {
 	}
 }
 
+func TestKeyAuthPemInsteadOfJsonKeyErrorHandling(t *testing.T) {
+	cfg := &config.Configuration{
+		ServiceAccountKey: "-----BEGIN PRIVATE KEY",
+	}
+	_, err := KeyAuth(cfg)
+	if err == nil {
+		t.Fatalf("error expected")
+	}
+	if !strings.HasSuffix(err.Error(), "Please provide it in JSON format.") {
+		t.Fatalf("expected to end with JSON format hint: %s", err)
+	}
+}
+
 func TestNoAuth(t *testing.T) {
 	for _, test := range []struct {
 		desc string