feat: Rate limit API token requests

600 per minute per token, in the Redis that sessions already require.
Cookie sessions are untouched. A Redis failure falls through rather than
refusing traffic — it is already a larger problem and should not become a
second outage.

server/internal/api/handlers.go

@@ -53,6 +53,7 @@ func RegisterRoutes(r *gin.Engine) {
 	// no-ops for cookie sessions. It is mounted here rather than per route so
 	// a route added later is covered by where it lives, not by memory.
 	apiGroup.Use(RequireScopes())
+	apiGroup.Use(RateLimitTokens())
 	// Deny by default: every non-GET route under /api is gated unless it is on
 	// the exemption list in licence.go. A route added later is covered because
 	// of where it is mounted, not because someone remembered.

server/internal/api/ratelimit.go

@@ -0,0 +1,57 @@
+package api
+
+import (
+	"net/http"
+	"strconv"
+	"time"
+
+	"gitea.hostxtra.co.uk/mrhid6/vantage/server/internal/auth"
+	"github.com/gin-gonic/gin"
+)
+
+// tokenRateLimit is per token per minute. It is not the general API
+// rate-limiting project: it is only enough that a runaway script cannot take an
+// instance down, and cookie sessions are deliberately untouched.
+const tokenRateLimit = 600
+
+// RateLimitTokens counts requests per token in a one-minute fixed window.
+//
+// A fixed window rather than a sliding one because the cost of a burst at a
+// boundary is a script running twice as fast for one second, and a sliding
+// window is a sorted set per token for that.
+func RateLimitTokens() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		if !auth.IsToken(c) {
+			c.Next()
+			return
+		}
+		rdb := auth.Redis()
+		if rdb == nil {
+			c.Next()
+			return
+		}
+
+		window := time.Now().UTC().Unix() / 60
+		key := "vantage:tokenrate:" + auth.TokenID(c) + ":" + strconv.FormatInt(window, 10)
+
+		count, err := rdb.Incr(c.Request.Context(), key).Result()
+		if err != nil {
+			// Redis is already required for sessions, so it being down is a
+			// larger problem than this. Do not turn it into a second outage.
+			c.Next()
+			return
+		}
+		if count == 1 {
+			rdb.Expire(c.Request.Context(), key, 2*time.Minute)
+		}
+		if count > tokenRateLimit {
+			c.Header("Retry-After", "60")
+			c.AbortWithStatusJSON(http.StatusTooManyRequests, gin.H{
+				"error": "rate limit exceeded for this API token",
+				"code":  "rate_limited",
+			})
+			return
+		}
+		c.Next()
+	}
+}

server/internal/auth/session.go

@@ -59,6 +59,11 @@ func PingRedis(ctx context.Context) error {
 	return rdb.Ping(ctx).Err()
 }
 
+// Redis exposes the session client for callers that need a counter rather than
+// a session. There is one Redis in this deployment and adding a second client
+// would double the connection pool for no reason.
+func Redis() *redis.Client { return rdb }
+
 func randomHex(n int) (string, error) {
 	b := make([]byte, n)
 	if _, err := rand.Read(b); err != nil {