feat(auth): host-based org resolution + session/host match guard

server/internal/auth/middleware.go

@@ -55,6 +55,12 @@ func Middleware() gin.HandlerFunc {
 		}
 
 		c.Set(ctxSessionKey, sess)
+
+		if hostOrg, ok := OrgFromHost(c); ok && hostOrg.OrgID != sess.OrgID {
+			c.AbortWithStatusJSON(http.StatusForbidden, gin.H{"error": "org host mismatch"})
+			return
+		}
+
 		c.Next()
 	}
 }

server/internal/auth/orghost.go

@@ -0,0 +1,66 @@
+package auth
+
+import (
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/mrhid6/vantage/server/internal/models"
+	"github.com/mrhid6/vantage/server/internal/services"
+)
+
+type cachedOrg struct {
+	org *models.Org
+	at  time.Time
+}
+
+var (
+	orgCacheMu sync.Mutex
+	orgCache   = map[string]cachedOrg{}
+)
+
+const orgCacheTTL = 60 * time.Second
+
+// hostSlug extracts the leftmost DNS label if the host is a subdomain of the
+// app root. Returns "" for the apex or an unknown host shape.
+func hostSlug(host string) string {
+	host = strings.ToLower(host)
+	if i := strings.IndexByte(host, ':'); i >= 0 {
+		host = host[:i]
+	}
+	// Expect <slug>.vantage.<...>; apex is vantage.<...>
+	parts := strings.Split(host, ".")
+	if len(parts) < 3 {
+		return ""
+	}
+	if parts[1] != "vantage" {
+		return ""
+	}
+	if parts[0] == "vantage" || parts[0] == "www" {
+		return ""
+	}
+	return parts[0]
+}
+
+func OrgFromHost(c *gin.Context) (*models.Org, bool) {
+	slug := hostSlug(c.Request.Host)
+	if slug == "" {
+		return nil, false
+	}
+	orgCacheMu.Lock()
+	if e, ok := orgCache[slug]; ok && time.Since(e.at) < orgCacheTTL {
+		orgCacheMu.Unlock()
+		return e.org, e.org != nil
+	}
+	orgCacheMu.Unlock()
+
+	org, err := services.GetOrgBySlug(slug)
+	if err != nil {
+		org = nil
+	}
+	orgCacheMu.Lock()
+	orgCache[slug] = cachedOrg{org: org, at: time.Now()}
+	orgCacheMu.Unlock()
+	return org, org != nil
+}