diff --git a/docs/rate-limiting.md b/docs/rate-limiting.md
index 8300355..6ab1498 100644
--- a/docs/rate-limiting.md
+++ b/docs/rate-limiting.md
@@ -4,6 +4,11 @@ Public read endpoints (`GET /api/markets`, `GET /api/leaderboard`) are throttled
 per client IP using a sliding-window counter. Authenticated requests that include
 a `Bearer` token bypass the limiter.
 
+Authentication endpoints under `/api/auth` are also rate-limited with a per-identity
+window (default 5 requests per minute) to reduce abuse from repeated challenge or
+verification attempts. The limiter uses the submitted Stellar address when present
+and falls back to the client IP otherwise.
+
 ## Configuration
 
 | Variable | Default | Description |
diff --git a/src/middleware/rateLimit.ts b/src/middleware/rateLimit.ts
index a2723a5..d28728b 100644
--- a/src/middleware/rateLimit.ts
+++ b/src/middleware/rateLimit.ts
@@ -153,6 +153,13 @@ export function createPerUserRateLimiter(options: Partial<Options> = {}): RateLi
     windowMs: 60 * 1000,
     limit: 60,
     ...options,
-    keyGenerator: (req: Request) => getAuthenticatedUserKey(req) ?? `ip:${getClientIp(req)}`,
+    keyGenerator: (req: Request) => {
+      const overrideKey = options.keyGenerator?.(req);
+      if (typeof overrideKey === "string" && overrideKey.trim().length > 0) {
+        return overrideKey;
+      }
+
+      return getAuthenticatedUserKey(req) ?? `ip:${getClientIp(req)}`;
+    },
   });
 }
diff --git a/src/routes/auth.ts b/src/routes/auth.ts
index 6305698..bf37e34 100644
--- a/src/routes/auth.ts
+++ b/src/routes/auth.ts
@@ -1,6 +1,7 @@
 import { Router } from "express";
 import { z } from "zod";
 import { StrKey } from "@stellar/stellar-sdk";
+import { createPerUserRateLimiter } from "../middleware/rateLimit";
 import {
   rotateRefreshToken,
   revokeFamily,
@@ -11,6 +12,23 @@ import { RouteErrorFactory } from "../errors";
 
 export const authRouter = Router();
 
+function getAuthRateLimitKey(req: { body?: unknown; socket?: { remoteAddress?: string | null } }): string {
+  const body = typeof req.body === "object" && req.body !== null ? req.body as Record<string, unknown> : undefined;
+  const stellarAddress = typeof body?.stellarAddress === "string" ? body.stellarAddress.trim() : "";
+
+  if (stellarAddress.length > 0) {
+    return `auth:${stellarAddress}`;
+  }
+
+  return `ip:${req.socket?.remoteAddress ?? "unknown"}`;
+}
+
+authRouter.use(createPerUserRateLimiter({
+  windowMs: 60 * 1000,
+  limit: 5,
+  keyGenerator: (req) => getAuthRateLimitKey(req),
+}));
+
 const refreshTokenBodySchema = z.object({
   refreshToken: z.string().min(1),
 });
diff --git a/tests/authChallenge.test.ts b/tests/authChallenge.test.ts
index bb30140..0cdc87c 100644
--- a/tests/authChallenge.test.ts
+++ b/tests/authChallenge.test.ts
@@ -6,6 +6,10 @@ process.env.PREDICTIFY_CONTRACT_ID = "CABC...";
 
 import request from "supertest";
 
+jest.mock("../src/services/auditService", () => ({
+  createAuditLog: jest.fn().mockResolvedValue(undefined),
+}));
+
 jest.mock("../src/services/authChallengeService", () => ({
   generateNonce: jest.fn(() => "aaaa"),
   computeExpiresAt: jest.fn(() => new Date()),
@@ -70,4 +74,26 @@ describe("POST /api/auth/challenge", () => {
     expect(res.status).toBe(400);
     expect(res.body.error.type).toBe("BadRequest");
   }, 10000);
+
+  it("rate limits repeated challenge attempts for the same authenticated identity", async () => {
+    const address = "GABSCDZCXMOO6CYNTHBGHAOE3RX72FRMNWK6O4FOXW6OBQATNWKBUUW6";
+
+    for (let index = 0; index < 5; index += 1) {
+      const res = await request(app)
+        .post("/api/auth/challenge")
+        .send({ stellarAddress: address });
+
+      if (index < 4) {
+        expect(res.status).toBe(201);
+      }
+    }
+
+    const res = await request(app)
+      .post("/api/auth/challenge")
+      .send({ stellarAddress: address });
+
+    expect(res.status).toBe(429);
+    expect(res.body.error.code).toBe("rate_limit_exceeded");
+    expect(res.body.error.retryAfter).toEqual(expect.any(Number));
+  }, 10000);
 });