x/oauth2: make DeviceAuth retrieval populate RetrieveError

Endpoints may return errors when attempting to request device authorization. Currently, these error codes are ignored and an otherwise empty RetrieveError returned. This change populates the RetrieveError similar to the oauth2 token exchange.

Fix golang/go#75759

Author: andig

deviceauth.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"mime"
 	"net/http"
 	"net/url"
 	"strings"
@@ -116,10 +117,27 @@ func retrieveDeviceAuth(ctx context.Context, c *Config, v url.Values) (*DeviceAu
 		return nil, fmt.Errorf("oauth2: cannot auth device: %v", err)
 	}
 	if code := r.StatusCode; code < 200 || code > 299 {
-		return nil, &RetrieveError{
+		retrieveError := &RetrieveError{
 			Response: r,
 			Body:     body,
 		}
+
+		content, _, _ := mime.ParseMediaType(r.Header.Get("Content-Type"))
+		switch content {
+		case "application/x-www-form-urlencoded", "text/plain":
+			// some endpoints return a query string
+			vals, err := url.ParseQuery(string(body))
+			if err != nil {
+				return nil, retrieveError
+			}
+			retrieveError.ErrorCode = vals.Get("error")
+			retrieveError.ErrorDescription = vals.Get("error_description")
+			retrieveError.ErrorURI = vals.Get("error_uri")
+		default:
+			json.Unmarshal(body, &retrieveError) // no error checks
+		}
+
+		return nil, retrieveError
 	}
 
 	da := &DeviceAuthResponse{}