refactor(feeds): extract atom feed builder + basic-auth validator for reuse

Splits the transport-agnostic cores out of the v1 echo handlers so the
v2 Huma endpoints can share them:

- AuthenticateFeedToken(s, username, password) holds the token
  validation (prefix/length guard, owner match, feeds scope, bot
  rejection); BasicAuth now creates the session and delegates to it.
- BuildNotificationsAtomFeed(s, u) renders the Atom XML;
  NotificationsAtomFeed reads the context user and delegates to it.
- AtomContentType is shared so both transports set the same header.

The v1 handlers keep identical observable behavior.

pkg/routes/feeds/auth.go

@@ -23,9 +23,9 @@ import (
 	"code.vikunja.io/api/pkg/log"
 	"code.vikunja.io/api/pkg/models"
 	"code.vikunja.io/api/pkg/user"
-	"xorm.io/xorm"
 
 	"github.com/labstack/echo/v5"
+	"xorm.io/xorm"
 )
 
 func checkAPIToken(s *xorm.Session, username, token string) (*user.User, error) {
@@ -50,35 +50,48 @@ func checkAPIToken(s *xorm.Session, username, token string) (*user.User, error)
 	return u, nil
 }
 
-// BasicAuth authenticates feed requests. Only API tokens are accepted —
-// password and LDAP credentials are rejected outright because feed URLs are
-// commonly exported, shared, or cached by feed readers.
-func BasicAuth(c *echo.Context, username, password string) (bool, error) {
+// AuthenticateFeedToken validates feed credentials against an existing session.
+// Only API tokens are accepted — password and LDAP credentials are rejected
+// outright because feed URLs are commonly exported, shared, or cached by feed
+// readers. It returns the authenticated user, or nil for any rejection so
+// callers can treat "invalid" and "unknown" identically.
+func AuthenticateFeedToken(s *xorm.Session, username, password string) (*user.User, error) {
 	if !strings.HasPrefix(password, models.APITokenPrefix) {
-		return false, nil
+		return nil, nil
 	}
 	// GetTokenFromTokenString slices password[len-8:] without a length check,
 	// so a stray "tk_" or other short prefix-only string would panic before
 	// the credentials could be rejected. Real tokens are far longer than
 	// prefix+8, so anything shorter is invalid by construction.
 	if len(password) < len(models.APITokenPrefix)+8 {
-		return false, nil
+		return nil, nil
 	}
 
-	s := db.NewSession()
-	defer s.Close()
-
 	u, err := checkAPIToken(s, username, password)
 	if err != nil {
 		log.Errorf("Error during API token auth for feeds: %v", err)
-		return false, nil
+		return nil, nil
 	}
 	if u == nil {
-		return false, nil
+		return nil, nil
 	}
 	if u.IsBot() {
 		log.Warningf("Feed auth rejected for bot user %d", u.ID)
-		return false, nil
+		return nil, nil
+	}
+
+	return u, nil
+}
+
+// BasicAuth authenticates feed requests for echo's BasicAuth middleware. The
+// validation logic is shared with the v2 handler via AuthenticateFeedToken.
+func BasicAuth(c *echo.Context, username, password string) (bool, error) {
+	s := db.NewSession()
+	defer s.Close()
+
+	u, err := AuthenticateFeedToken(s, username, password)
+	if err != nil || u == nil {
+		return false, err
 	}
 
 	c.Set("userBasicAuth", u)

pkg/routes/feeds/handler.go

@@ -30,24 +30,22 @@ import (
 
 	"github.com/gorilla/feeds"
 	"github.com/labstack/echo/v5"
+	"xorm.io/xorm"
 )
 
 const feedItemLimit = 50
 
-// NotificationsAtomFeed serves the authenticated user's notifications as an
-// Atom feed. Notifications are not marked as read by being fetched here.
-func NotificationsAtomFeed(c *echo.Context) error {
-	u, ok := c.Get("userBasicAuth").(*user.User)
-	if !ok {
-		return echo.NewHTTPError(http.StatusUnauthorized, http.StatusText(http.StatusUnauthorized))
-	}
-
-	s := db.NewSession()
-	defer s.Close()
+// AtomContentType is the content type of the notifications Atom feed. Shared so
+// the v1 echo handler and the v2 Huma op set the same header.
+const AtomContentType = "application/atom+xml; charset=utf-8"
 
+// BuildNotificationsAtomFeed renders the user's latest notifications as Atom XML
+// against an existing session. Notifications are not marked as read by being
+// fetched here. Shared by the v1 echo handler and the v2 Huma op.
+func BuildNotificationsAtomFeed(s *xorm.Session, u *user.User) (string, error) {
 	rows, _, _, err := notifications.GetNotificationsForUser(s, u.ID, feedItemLimit, 0)
 	if err != nil {
-		return err
+		return "", err
 	}
 
 	publicURL := config.ServicePublicURL.GetString()
@@ -85,11 +83,25 @@ func NotificationsAtomFeed(c *echo.Context) error {
 		})
 	}
 
-	atom, err := feed.ToAtom()
+	return feed.ToAtom()
+}
+
+// NotificationsAtomFeed serves the authenticated user's notifications as an
+// Atom feed. Notifications are not marked as read by being fetched here.
+func NotificationsAtomFeed(c *echo.Context) error {
+	u, ok := c.Get("userBasicAuth").(*user.User)
+	if !ok {
+		return echo.NewHTTPError(http.StatusUnauthorized, http.StatusText(http.StatusUnauthorized))
+	}
+
+	s := db.NewSession()
+	defer s.Close()
+
+	atom, err := BuildNotificationsAtomFeed(s, u)
 	if err != nil {
 		return err
 	}
 
-	c.Response().Header().Set(echo.HeaderContentType, "application/atom+xml; charset=utf-8")
+	c.Response().Header().Set(echo.HeaderContentType, AtomContentType)
 	return c.String(http.StatusOK, atom)
 }