Send a blogger to their own dashboard from another blog's /webadmin

Typing /webadmin on someone else's blog while logged in (or logging in
from there) landed on /b/<their-sub>/ and a 403 "This is not your blog."
Both login paths now go through landing(), which swaps a next that points
at a blog the user cannot manage for /dashboard; superadmins keep going
where they asked.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Sd8UPWrvyYCLj97JexNw3A

1 files changed, 21 insertions, 9 deletions

diff --git a/internal/web/handlers_auth.go b/internal/web/handlers_auth.go
index 3030f11..1321b2d 100644
--- a/internal/web/handlers_auth.go
+++ b/internal/web/handlers_auth.go
@@ -12,16 +12,31 @@ import (
 
 func (s *Server) handleLoginForm(w http.ResponseWriter, r *http.Request) {
 	next := safeNext(r.URL.Query().Get("next"))
-	if currentUser(r) != nil {
-		if next == "" {
-			next = "/dashboard"
-		}
-		http.Redirect(w, r, next, http.StatusSeeOther)
+	if u := currentUser(r); u != nil {
+		http.Redirect(w, r, s.landing(r, u, next), http.StatusSeeOther)
 		return
 	}
 	s.render(w, r, "auth/login.html", map[string]any{"next": next})
 }
 
+// landing is where a user goes once logged in: next, unless that is another
+// blogger's dashboard — someone typing /webadmin on a blog that is not theirs
+// gets their own dashboard, not a 403.
+func (s *Server) landing(r *http.Request, u *store.User, next string) string {
+	if next == "" {
+		return "/dashboard"
+	}
+	if rest, ok := strings.CutPrefix(next, "/b/"); ok && !u.IsSuperadmin() {
+		sub, _, _ := strings.Cut(rest, "/")
+		sub, _, _ = strings.Cut(sub, "?")
+		blog, err := s.st.BlogBySubdomain(r.Context(), sub)
+		if err != nil || blog.OwnerID != u.ID {
+			return "/dashboard"
+		}
+	}
+	return next
+}
+
 // handleWebadminRedirect serves /webadmin on a blog's own host: the login page
 // lives on the root domain, so bounce there and come back to this blog's dashboard.
 func (s *Server) handleWebadminRedirect(w http.ResponseWriter, r *http.Request) {
@@ -57,10 +72,7 @@ func (s *Server) handleLogin(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	auth.SetSessionCookie(w, tok)
-	if next == "" {
-		next = "/dashboard"
-	}
-	http.Redirect(w, r, next, http.StatusSeeOther)
+	http.Redirect(w, r, s.landing(r, u, next), http.StatusSeeOther)
 }
 
 func (s *Server) handleLogout(w http.ResponseWriter, r *http.Request) {