diff --git a/apps/web/src/http-error.ts b/apps/web/src/http-error.ts
new file mode 100644
index 0000000..63543aa
--- /dev/null
+++ b/apps/web/src/http-error.ts
@@ -0,0 +1,9 @@
+export class HttpError extends Error {
+  constructor(
+    readonly statusCode: number,
+    readonly code: string,
+    message: string,
+  ) {
+    super(message);
+  }
+}
diff --git a/apps/web/src/http-security.test.ts b/apps/web/src/http-security.test.ts
new file mode 100644
index 0000000..7f23828
--- /dev/null
+++ b/apps/web/src/http-security.test.ts
@@ -0,0 +1,101 @@
+import assert from "node:assert/strict";
+import type { IncomingMessage } from "node:http";
+import test from "node:test";
+import { HttpError } from "./http-error.js";
+import {
+  InMemoryRateLimiter,
+  assertTrustedOrigin,
+  getRateLimitClientIp,
+  readJsonBody,
+} from "./http-security.js";
+
+test("readJsonBody parses JSON payloads within the configured limit", async () => {
+  const request = createMockRequest({
+    headers: {
+      "content-length": "17",
+    },
+    chunks: ['{"hello":"world"}'],
+  });
+
+  const body = await readJsonBody(request, { maxBytes: 64 });
+
+  assert.deepEqual(body, {
+    hello: "world",
+  });
+});
+
+test("readJsonBody rejects payloads larger than the configured limit", async () => {
+  const request = createMockRequest({
+    headers: {
+      "content-length": "128",
+    },
+    chunks: ['{"hello":"world"}'],
+  });
+
+  await assert.rejects(
+    readJsonBody(request, { maxBytes: 32 }),
+    (error: unknown) =>
+      error instanceof HttpError &&
+      error.statusCode === 413 &&
+      error.code === "payload_too_large",
+  );
+});
+
+test("InMemoryRateLimiter blocks after the configured request budget is exhausted", () => {
+  const limiter = new InMemoryRateLimiter();
+  const policy = {
+    id: "auth",
+    windowMs: 60_000,
+    maxRequests: 2,
+  };
+
+  assert.deepEqual(limiter.consume(policy, "ip:127.0.0.1", 1_000), { allowed: true });
+  assert.deepEqual(limiter.consume(policy, "ip:127.0.0.1", 2_000), { allowed: true });
+
+  const blocked = limiter.consume(policy, "ip:127.0.0.1", 3_000);
+
+  assert.equal(blocked.allowed, false);
+  assert.equal(blocked.retryAfterSeconds, 58);
+});
+
+test("assertTrustedOrigin accepts configured origins and requires browser origin metadata", () => {
+  const request = createMockRequest({
+    headers: {
+      origin: "https://app.nproxy.test",
+      "x-forwarded-for": "198.51.100.7, 198.51.100.8",
+    },
+  });
+
+  assert.doesNotThrow(() =>
+    assertTrustedOrigin(request, ["https://app.nproxy.test", "https://admin.nproxy.test"]),
+  );
+  assert.equal(getRateLimitClientIp(request), "198.51.100.7");
+
+  assert.throws(
+    () => assertTrustedOrigin(createMockRequest(), ["https://app.nproxy.test"]),
+    (error: unknown) =>
+      error instanceof HttpError &&
+      error.statusCode === 403 &&
+      error.code === "csrf_origin_required",
+  );
+});
+
+function createMockRequest(input?: {
+  headers?: IncomingMessage["headers"];
+  chunks?: Array<string | Uint8Array>;
+  remoteAddress?: string;
+}): IncomingMessage {
+  const chunks = input?.chunks ?? [];
+
+  return {
+    headers: input?.headers ?? {},
+    socket: {
+      remoteAddress: input?.remoteAddress ?? "127.0.0.1",
+    },
+    async *[Symbol.asyncIterator]() {
+      for (const chunk of chunks) {
+        yield typeof chunk === "string" ? Buffer.from(chunk) : chunk;
+      }
+    },
+  } as IncomingMessage;
+}
diff --git a/apps/web/src/http-security.ts b/apps/web/src/http-security.ts
new file mode 100644
index 0000000..7489deb
--- /dev/null
+++ b/apps/web/src/http-security.ts
@@ -0,0 +1,177 @@
+import type { IncomingMessage } from "node:http";
+import { HttpError } from "./http-error.js";
+
+export interface JsonBodyOptions {
+  maxBytes: number;
+}
+
+export interface RateLimitPolicy {
+  id: string;
+  windowMs: number;
+  maxRequests: number;
+}
+
+export interface RateLimitDecision {
+  allowed: boolean;
+  retryAfterSeconds?: number;
+}
+
+interface RateLimitEntry {
+  count: number;
+  resetAt: number;
+}
+
+export async function readJsonBody(
+  request: IncomingMessage,
+  options: JsonBodyOptions,
+): Promise<unknown> {
+  const declaredLength = readContentLength(request);
+
+  if (declaredLength !== null && declaredLength > options.maxBytes) {
+    throw new HttpError(
+      413,
+      "payload_too_large",
+      `Request body must not exceed ${options.maxBytes} bytes.`,
+    );
+  }
+
+  const chunks: Uint8Array[] = [];
+  let totalBytes = 0;
+
+  for await (const chunk of request) {
+    const buffer = typeof chunk === "string" ? Buffer.from(chunk) : chunk;
+    totalBytes += buffer.byteLength;
+
+    if (totalBytes > options.maxBytes) {
+      throw new HttpError(
+        413,
+        "payload_too_large",
+        `Request body must not exceed ${options.maxBytes} bytes.`,
+      );
+    }
+
+    chunks.push(buffer);
+  }
+
+  if (chunks.length === 0) {
+    throw new HttpError(400, "invalid_json", "Request body must not be empty.");
+  }
+
+  try {
+    return JSON.parse(Buffer.concat(chunks).toString("utf8")) as unknown;
+  } catch {
+    throw new HttpError(400, "invalid_json", "Request body must be valid JSON.");
+  }
+}
+
+export class InMemoryRateLimiter {
+  private readonly entries = new Map<string, RateLimitEntry>();
+
+  consume(policy: RateLimitPolicy, key: string, now = Date.now()): RateLimitDecision {
+    const bucketKey = `${policy.id}:${key}`;
+    const existing = this.entries.get(bucketKey);
+
+    if (!existing || existing.resetAt <= now) {
+      this.entries.set(bucketKey, {
+        count: 1,
+        resetAt: now + policy.windowMs,
+      });
+      return { allowed: true };
+    }
+
+    if (existing.count >= policy.maxRequests) {
+      return {
+        allowed: false,
+        retryAfterSeconds: Math.max(1, Math.ceil((existing.resetAt - now) / 1000)),
+      };
+    }
+
+    existing.count += 1;
+    this.entries.set(bucketKey, existing);
+    return { allowed: true };
+  }
+}
+
+export function getRateLimitClientIp(request: IncomingMessage): string {
+  const forwardedFor = request.headers["x-forwarded-for"];
+  const headerValue = Array.isArray(forwardedFor) ? forwardedFor[0] : forwardedFor;
+
+  if (headerValue) {
+    const firstIp = headerValue
+      .split(",")
+      .map((part) => part.trim())
+      .find((part) => part.length > 0);
+
+    if (firstIp) {
+      return firstIp;
+    }
+  }
+
+  return request.socket.remoteAddress ?? "unknown";
+}
+
+export function assertTrustedOrigin(
+  request: IncomingMessage,
+  allowedOrigins: readonly string[],
+): void {
+  const candidate = readRequestOrigin(request);
+
+  if (!candidate) {
+    throw new HttpError(
+      403,
+      "csrf_origin_required",
+      "State-changing requests must include an Origin or Referer header.",
+    );
+  }
+
+  if (!allowedOrigins.includes(candidate)) {
+    throw new HttpError(
+      403,
+      "csrf_origin_invalid",
+      "State-changing requests must originate from an allowed nproxy origin.",
+    );
+  }
+}
+
+function readRequestOrigin(request: IncomingMessage): string | null {
+  const originHeader = request.headers.origin;
+  const rawOrigin = Array.isArray(originHeader) ? originHeader[0] : originHeader;
+
+  if (rawOrigin) {
+    try {
+      return new URL(rawOrigin).origin;
+    } catch {
+      throw new HttpError(400, "invalid_origin", "Origin header must be a valid URL.");
+    }
+  }
+
+  const refererHeader = request.headers.referer;
+  const rawReferer = Array.isArray(refererHeader) ? refererHeader[0] : refererHeader;
+
+  if (!rawReferer) {
+    return null;
+  }
+
+  try {
+    return new URL(rawReferer).origin;
+  } catch {
+    throw new HttpError(400, "invalid_referer", "Referer header must be a valid URL.");
+  }
+}
+
+function readContentLength(request: IncomingMessage): number | null {
+  const contentLength = request.headers["content-length"];
+  const rawValue = Array.isArray(contentLength) ? contentLength[0] : contentLength;
+
+  if (!rawValue) {
+    return null;
+  }
+
+  const parsed = Number.parseInt(rawValue, 10);
+
+  if (!Number.isFinite(parsed) || parsed < 0) {
+    throw new HttpError(400, "invalid_content_length", "Content-Length must be valid.");
+  }
+
+  return parsed;
+}
diff --git a/apps/web/src/main.ts b/apps/web/src/main.ts
index 69aefe3..f4ad34a 100644
--- a/apps/web/src/main.ts
+++ b/apps/web/src/main.ts
@@ -17,9 +17,23 @@ import {
   AuthError,
   GenerationRequestError,
   createGenerationRequest,
-  type CreateGenerationRequestInput,
 } from "@nproxy/domain";
 import { serializePublicAccountOverview } from "./account-response.js";
+import { HttpError } from "./http-error.js";
+import {
+  InMemoryRateLimiter,
+  assertTrustedOrigin,
+  getRateLimitClientIp,
+  readJsonBody,
+  type RateLimitPolicy,
+} from "./http-security.js";
+import {
+  defaultGenerationRequestConstraints,
+  mapCreateGenerationRequestInput,
+  readAuthPayload,
+  readEmailOnlyPayload,
+  readPasswordResetConfirmPayload,
+} from "./request-parsing.js";
 
 const config = loadConfig();
 const port = Number.parseInt(process.env.PORT ?? "3000", 10);
@@ -30,6 +44,23 @@ const generationStore = createPrismaGenerationStore(prisma);
 const emailTransport = createEmailTransport(config.email);
 const paymentProviderAdapter = createPaymentProviderAdapter(config.payment);
 const sessionCookieName = "nproxy_session";
+const maxJsonBodyBytes = 16 * 1024;
+const rateLimiter = new InMemoryRateLimiter();
+const mutationAllowedOrigins = [config.urls.appBaseUrl.origin, config.urls.adminBaseUrl.origin];
+const authRateLimitPolicy: RateLimitPolicy = {
+  id: "auth",
+  windowMs: 60_000,
+  maxRequests: 10,
+};
+const generationRateLimitPolicy: RateLimitPolicy = {
+  id: "generation",
+  windowMs: 60_000,
+  maxRequests: 30,
+};
+const generationRequestConstraints = {
+  ...defaultGenerationRequestConstraints,
+  providerModels: [config.provider.nanoBananaDefaultModel],
+};
 
 const server = createServer(async (request, response) => {
   try {
@@ -39,7 +70,8 @@ const server = createServer(async (request, response) => {
     }
 
     if (request.method === "POST" && request.url === "/api/auth/register") {
-      const body = await readJsonBody(request);
+      enforceRateLimit(request, authRateLimitPolicy);
+      const body = await readJsonBody(request, { maxBytes: maxJsonBodyBytes });
       const payload = readAuthPayload(body);
       const session = await authStore.registerUser({
         email: payload.email,
@@ -57,7 +89,8 @@ const server = createServer(async (request, response) => {
     }
 
     if (request.method === "POST" && request.url === "/api/auth/login") {
-      const body = await readJsonBody(request);
+      enforceRateLimit(request, authRateLimitPolicy);
+      const body = await readJsonBody(request, { maxBytes: maxJsonBodyBytes });
       const payload = readAuthPayload(body);
       const session = await authStore.loginUser({
         email: payload.email,
@@ -75,7 +108,8 @@ const server = createServer(async (request, response) => {
     }
 
     if (request.method === "POST" && request.url === "/api/auth/password-reset/request") {
-      const body = await readJsonBody(request);
+      enforceRateLimit(request, authRateLimitPolicy);
+      const body = await readJsonBody(request, { maxBytes: maxJsonBodyBytes });
       const payload = readEmailOnlyPayload(body);
       const challenge = await authStore.createPasswordResetChallenge({
         email: payload.email,
@@ -103,7 +137,8 @@ const server = createServer(async (request, response) => {
     }
 
     if (request.method === "POST" && request.url === "/api/auth/password-reset/confirm") {
-      const body = await readJsonBody(request);
+      enforceRateLimit(request, authRateLimitPolicy);
+      const body = await readJsonBody(request, { maxBytes: maxJsonBodyBytes });
       const payload = readPasswordResetConfirmPayload(body);
 
       await authStore.resetPassword({
@@ -120,6 +155,7 @@ const server = createServer(async (request, response) => {
 
     if (request.method === "POST" && request.url === "/api/auth/logout") {
       const authenticatedSession = await requireAuthenticatedSession(request);
+      assertTrustedOrigin(request, mutationAllowedOrigins);
 
       await authStore.revokeSession(authenticatedSession.token);
 
@@ -176,6 +212,7 @@ const server = createServer(async (request, response) => {
 
     if (request.method === "POST" && request.url === "/api/billing/invoices") {
       const authenticatedSession = await requireAuthenticatedSession(request);
+      assertTrustedOrigin(request, mutationAllowedOrigins);
       const invoice = await billingStore.createSubscriptionInvoice({
         userId: authenticatedSession.user.id,
         paymentProvider: config.payment.provider,
@@ -189,6 +226,7 @@ const server = createServer(async (request, response) => {
 
     if (request.method === "POST" && request.url === "/api/auth/logout-all") {
       const authenticatedSession = await requireAuthenticatedSession(request);
+      assertTrustedOrigin(request, mutationAllowedOrigins);
       const revokedCount = await authStore.revokeAllUserSessions({
         userId: authenticatedSession.user.id,
         exceptSessionId: authenticatedSession.session.id,
@@ -206,6 +244,7 @@ const server = createServer(async (request, response) => {
 
       if (invoiceMarkPaidMatch) {
         const authenticatedSession = await requireAuthenticatedSession(request);
+        assertTrustedOrigin(request, mutationAllowedOrigins);
 
         if (!authenticatedSession.user.isAdmin) {
           throw new HttpError(403, "forbidden", "Admin session is required.");
@@ -231,6 +270,7 @@ const server = createServer(async (request, response) => {
 
       if (sessionMatch) {
         const authenticatedSession = await requireAuthenticatedSession(request);
+        assertTrustedOrigin(request, mutationAllowedOrigins);
         const sessionId = decodeURIComponent(sessionMatch[1] ?? "");
 
         if (sessionId === authenticatedSession.session.id) {
@@ -261,8 +301,18 @@ const server = createServer(async (request, response) => {
 
     if (request.method === "POST" && request.url === "/api/generations") {
       const authenticatedSession = await requireAuthenticatedSession(request);
-      const body = await readJsonBody(request);
-      const requestInput = mapCreateGenerationRequestInput(body, authenticatedSession.user.id);
+      assertTrustedOrigin(request, mutationAllowedOrigins);
+      enforceRateLimit(
+        request,
+        generationRateLimitPolicy,
+        `user:${authenticatedSession.user.id}:${getRateLimitClientIp(request)}`,
+      );
+      const body = await readJsonBody(request, { maxBytes: maxJsonBodyBytes });
+      const requestInput = mapCreateGenerationRequestInput(
+        body,
+        authenticatedSession.user.id,
+        generationRequestConstraints,
+      );
       const result = await createGenerationRequest(generationStore, requestInput);
 
       sendJson(response, result.reusedExistingRequest ? 200 : 201, {
@@ -340,133 +390,6 @@ process.once("SIGINT", async () => {
   process.exit(0);
 });
 
-async function readJsonBody(
-  request: IncomingMessage,
-): Promise<unknown> {
-  const chunks: Uint8Array[] = [];
-
-  for await (const chunk of request) {
-    chunks.push(typeof chunk === "string" ? Buffer.from(chunk) : chunk);
-  }
-
-  if (chunks.length === 0) {
-    throw new HttpError(400, "invalid_json", "Request body must not be empty.");
-  }
-
-  const rawBody = Buffer.concat(chunks).toString("utf8");
-
-  try {
-    return JSON.parse(rawBody) as unknown;
-  } catch {
-    throw new HttpError(400, "invalid_json", "Request body must be valid JSON.");
-  }
-}
-
-function readAuthPayload(body: unknown): { email: string; password: string } {
-  if (!body || typeof body !== "object") {
-    throw new HttpError(400, "invalid_body", "Request body must be a JSON object.");
-  }
-
-  const payload = body as Record<string, unknown>;
-
-  return {
-    email: readRequiredString(payload.email, "email"),
-    password: readRequiredString(payload.password, "password"),
-  };
-}
-
-function readEmailOnlyPayload(body: unknown): { email: string } {
-  if (!body || typeof body !== "object") {
-    throw new HttpError(400, "invalid_body", "Request body must be a JSON object.");
-  }
-
-  const payload = body as Record<string, unknown>;
-
-  return {
-    email: readRequiredString(payload.email, "email"),
-  };
-}
-
-function readPasswordResetConfirmPayload(
-  body: unknown,
-): { token: string; password: string } {
-  if (!body || typeof body !== "object") {
-    throw new HttpError(400, "invalid_body", "Request body must be a JSON object.");
-  }
-
-  const payload = body as Record<string, unknown>;
-
-  return {
-    token: readRequiredString(payload.token, "token"),
-    password: readRequiredString(payload.password, "password"),
-  };
-}
-
-function mapCreateGenerationRequestInput(
-  body: unknown,
-  userId: string,
-): CreateGenerationRequestInput {
-  if (!body || typeof body !== "object") {
-    throw new HttpError(400, "invalid_body", "Request body must be a JSON object.");
-  }
-
-  const payload = body as Record<string, unknown>;
-
-  return {
-    userId,
-    mode: readGenerationMode(payload.mode),
-    providerModel: readRequiredString(payload.providerModel, "providerModel"),
-    prompt: readRequiredString(payload.prompt, "prompt"),
-    resolutionPreset: readRequiredString(payload.resolutionPreset, "resolutionPreset"),
-    batchSize: readRequiredInteger(payload.batchSize, "batchSize"),
-    ...(payload.sourceImageKey !== undefined
-      ? { sourceImageKey: readRequiredString(payload.sourceImageKey, "sourceImageKey") }
-      : {}),
-    ...(payload.imageStrength !== undefined
-      ? { imageStrength: readRequiredNumber(payload.imageStrength, "imageStrength") }
-      : {}),
-    ...(payload.idempotencyKey !== undefined
-      ? { idempotencyKey: readRequiredString(payload.idempotencyKey, "idempotencyKey") }
-      : {}),
-  };
-}
-
-function readGenerationMode(value: unknown): CreateGenerationRequestInput["mode"] {
-  if (value === "text_to_image" || value === "image_to_image") {
-    return value;
-  }
-
-  throw new HttpError(
-    400,
-    "invalid_mode",
-    'mode must be "text_to_image" or "image_to_image".',
-  );
-}
-
-function readRequiredString(value: unknown, field: string): string {
-  if (typeof value !== "string" || value.trim().length === 0) {
-    throw new HttpError(400, "invalid_field", `${field} must be a non-empty string.`);
-  }
-
-  return value;
-}
-
-function readRequiredInteger(value: unknown, field: string): number {
-  if (typeof value !== "number" || !Number.isInteger(value)) {
-    throw new HttpError(400, "invalid_field", `${field} must be an integer.`);
-  }
-
-  return value;
-}
-
-function readRequiredNumber(value: unknown, field: string): number {
-  if (typeof value !== "number" || Number.isNaN(value)) {
-    throw new HttpError(400, "invalid_field", `${field} must be a number.`);
-  }
-
-  return value;
-}
-
 function serializeAuthenticatedUser(user: {
   id: string;
   email: string;
@@ -631,7 +554,7 @@ function createSessionCookie(token: string, expiresAt: Date): string {
     `${sessionCookieName}=${encodeURIComponent(token)}`,
     "Path=/",
     "HttpOnly",
-    "SameSite=Lax",
+    "SameSite=Strict",
     "Secure",
     `Expires=${expiresAt.toUTCString()}`,
   ].join("; ");
@@ -642,7 +565,7 @@ function clearSessionCookie(): string {
     `${sessionCookieName}=`,
     "Path=/",
     "HttpOnly",
-    "SameSite=Lax",
+    "SameSite=Strict",
     "Secure",
     "Expires=Thu, 01 Jan 1970 00:00:00 GMT",
   ].join("; ");
@@ -739,12 +662,18 @@ function sendJson(
   response.end(JSON.stringify(payload));
 }
 
-class HttpError extends Error {
-  constructor(
-    readonly statusCode: number,
-    readonly code: string,
-    message: string,
-  ) {
-    super(message);
+function enforceRateLimit(
+  request: IncomingMessage,
+  policy: RateLimitPolicy,
+  key = getRateLimitClientIp(request),
+): void {
+  const result = rateLimiter.consume(policy, key);
+
+  if (!result.allowed) {
+    throw new HttpError(
+      429,
+      "rate_limited",
+      `Retry after ${result.retryAfterSeconds ?? 1} seconds.`,
+    );
   }
 }
diff --git a/apps/web/src/request-parsing.test.ts b/apps/web/src/request-parsing.test.ts
new file mode 100644
index 0000000..621f41e
--- /dev/null
+++ b/apps/web/src/request-parsing.test.ts
@@ -0,0 +1,127 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+import { HttpError } from "./http-error.js";
+import {
+  defaultGenerationRequestConstraints,
+  mapCreateGenerationRequestInput,
+} from "./request-parsing.js";
+
+const generationRequestConstraints = {
+  ...defaultGenerationRequestConstraints,
+  providerModels: ["nano-banana"],
+};
+
+test("mapCreateGenerationRequestInput accepts supported generation options", () => {
+  const parsed = mapCreateGenerationRequestInput(
+    {
+      mode: "image_to_image",
+      providerModel: "nano-banana",
+      prompt: "sharpen this",
+      resolutionPreset: "1024",
+      batchSize: 2,
+      sourceImageKey: "uploads/source.png",
+      imageStrength: 0.4,
+      idempotencyKey: "req-1",
+    },
+    "user_1",
+    generationRequestConstraints,
+  );
+
+  assert.deepEqual(parsed, {
+    userId: "user_1",
+    mode: "image_to_image",
+    providerModel: "nano-banana",
+    prompt: "sharpen this",
+    resolutionPreset: "1024",
+    batchSize: 2,
+    sourceImageKey: "uploads/source.png",
+    imageStrength: 0.4,
+    idempotencyKey: "req-1",
+  });
+});
+
+test("mapCreateGenerationRequestInput rejects unsupported provider models", () => {
+  assert.throws(
+    () =>
+      mapCreateGenerationRequestInput(
+        {
+          mode: "text_to_image",
+          providerModel: "other-model",
+          prompt: "hello",
+          resolutionPreset: "1024",
+          batchSize: 1,
+        },
+        "user_1",
+        generationRequestConstraints,
+      ),
+    (error: unknown) =>
+      error instanceof HttpError &&
+      error.statusCode === 400 &&
+      error.message === "providerModel must be one of: nano-banana.",
+  );
+});
+
+test("mapCreateGenerationRequestInput rejects unsupported resolution presets", () => {
+  assert.throws(
+    () =>
+      mapCreateGenerationRequestInput(
+        {
+          mode: "text_to_image",
+          providerModel: "nano-banana",
+          prompt: "hello",
+          resolutionPreset: "2048",
+          batchSize: 1,
+        },
+        "user_1",
+        generationRequestConstraints,
+      ),
+    (error: unknown) =>
+      error instanceof HttpError &&
+      error.statusCode === 400 &&
+      error.message === "resolutionPreset must be one of: 1024.",
+  );
+});
+
+test("mapCreateGenerationRequestInput rejects batch sizes outside the allowed range", () => {
+  assert.throws(
+    () =>
+      mapCreateGenerationRequestInput(
+        {
+          mode: "text_to_image",
+          providerModel: "nano-banana",
+          prompt: "hello",
+          resolutionPreset: "1024",
+          batchSize: 5,
+        },
+        "user_1",
+        generationRequestConstraints,
+      ),
+    (error: unknown) =>
+      error instanceof HttpError &&
+      error.statusCode === 400 &&
+      error.message === "batchSize must be between 1 and 4.",
+  );
+});
+
+test("mapCreateGenerationRequestInput rejects image strengths outside the supported range", () => {
+  assert.throws(
+    () =>
+      mapCreateGenerationRequestInput(
+        {
+          mode: "image_to_image",
+          providerModel: "nano-banana",
+          prompt: "hello",
+          resolutionPreset: "1024",
+          batchSize: 1,
+          sourceImageKey: "uploads/source.png",
+          imageStrength: 1.5,
+        },
+        "user_1",
+        generationRequestConstraints,
+      ),
+    (error: unknown) =>
+      error instanceof HttpError &&
+      error.statusCode === 400 &&
+      error.message === "imageStrength must be between 0 and 1.",
+  );
+});
diff --git a/apps/web/src/request-parsing.ts b/apps/web/src/request-parsing.ts
new file mode 100644
index 0000000..4552c88
--- /dev/null
+++ b/apps/web/src/request-parsing.ts
@@ -0,0 +1,184 @@
+import type { CreateGenerationRequestInput } from "@nproxy/domain";
+import { HttpError } from "./http-error.js";
+
+export interface GenerationRequestConstraints {
+  providerModels: readonly string[];
+  resolutionPresets: readonly string[];
+  minBatchSize: number;
+  maxBatchSize: number;
+  minImageStrength: number;
+  maxImageStrength: number;
+}
+
+export const defaultGenerationRequestConstraints: Omit<
+  GenerationRequestConstraints,
+  "providerModels"
+> = {
+  resolutionPresets: ["1024"],
+  minBatchSize: 1,
+  maxBatchSize: 4,
+  minImageStrength: 0,
+  maxImageStrength: 1,
+};
+
+export function readAuthPayload(body: unknown): { email: string; password: string } {
+  const payload = readObjectBody(body);
+
+  return {
+    email: readRequiredString(payload.email, "email"),
+    password: readRequiredString(payload.password, "password"),
+  };
+}
+
+export function readEmailOnlyPayload(body: unknown): { email: string } {
+  const payload = readObjectBody(body);
+
+  return {
+    email: readRequiredString(payload.email, "email"),
+  };
+}
+
+export function readPasswordResetConfirmPayload(
+  body: unknown,
+): { token: string; password: string } {
+  const payload = readObjectBody(body);
+
+  return {
+    token: readRequiredString(payload.token, "token"),
+    password: readRequiredString(payload.password, "password"),
+  };
+}
+
+export function mapCreateGenerationRequestInput(
+  body: unknown,
+  userId: string,
+  constraints: GenerationRequestConstraints,
+): CreateGenerationRequestInput {
+  const payload = readObjectBody(body);
+
+  return {
+    userId,
+    mode: readGenerationMode(payload.mode),
+    providerModel: readSupportedString(
+      payload.providerModel,
+      "providerModel",
+      constraints.providerModels,
+    ),
+    prompt: readRequiredString(payload.prompt, "prompt"),
+    resolutionPreset: readSupportedString(
+      payload.resolutionPreset,
+      "resolutionPreset",
+      constraints.resolutionPresets,
+    ),
+    batchSize: readBoundedInteger(
+      payload.batchSize,
+      "batchSize",
+      constraints.minBatchSize,
+      constraints.maxBatchSize,
+    ),
+    ...(payload.sourceImageKey !== undefined
+      ? { sourceImageKey: readRequiredString(payload.sourceImageKey, "sourceImageKey") }
+      : {}),
+    ...(payload.imageStrength !== undefined
+      ? {
+          imageStrength: readBoundedNumber(
+            payload.imageStrength,
+            "imageStrength",
+            constraints.minImageStrength,
+            constraints.maxImageStrength,
+          ),
+        }
+      : {}),
+    ...(payload.idempotencyKey !== undefined
+      ? { idempotencyKey: readRequiredString(payload.idempotencyKey, "idempotencyKey") }
+      : {}),
+  };
+}
+
+function readObjectBody(body: unknown): Record<string, unknown> {
+  if (!body || typeof body !== "object" || Array.isArray(body)) {
+    throw new HttpError(400, "invalid_body", "Request body must be a JSON object.");
+  }
+
+  return body as Record<string, unknown>;
+}
+
+function readGenerationMode(value: unknown): CreateGenerationRequestInput["mode"] {
+  if (value === "text_to_image" || value === "image_to_image") {
+    return value;
+  }
+
+  throw new HttpError(
+    400,
+    "invalid_mode",
+    'mode must be "text_to_image" or "image_to_image".',
+  );
+}
+
+function readRequiredString(value: unknown, field: string): string {
+  if (typeof value !== "string" || value.trim().length === 0) {
+    throw new HttpError(400, "invalid_field", `${field} must be a non-empty string.`);
+  }
+
+  return value;
+}
+
+function readSupportedString(
+  value: unknown,
+  field: string,
+  supportedValues: readonly string[],
+): string {
+  const parsed = readRequiredString(value, field);
+
+  if (!supportedValues.includes(parsed)) {
+    throw new HttpError(
+      400,
+      "invalid_field",
+      `${field} must be one of: ${supportedValues.join(", ")}.`,
+    );
+  }
+
+  return parsed;
+}
+
+function readBoundedInteger(
+  value: unknown,
+  field: string,
+  min: number,
+  max: number,
+): number {
+  if (typeof value !== "number" || !Number.isInteger(value)) {
+    throw new HttpError(400, "invalid_field", `${field} must be an integer.`);
+  }
+
+  if (value < min || value > max) {
+    throw new HttpError(
+      400,
+      "invalid_field",
+      `${field} must be between ${min} and ${max}.`,
+    );
+  }
+
+  return value;
+}
+
+function readBoundedNumber(
+  value: unknown,
+  field: string,
+  min: number,
+  max: number,
+): number {
+  if (typeof value !== "number" || Number.isNaN(value)) {
+    throw new HttpError(400, "invalid_field", `${field} must be a number.`);
+  }
+
+  if (value < min || value > max) {
+    throw new HttpError(
+      400,
+      "invalid_field",
+      `${field} must be between ${min} and ${max}.`,
+    );
+  }
+
+  return value;
+}
diff --git a/docs/architecture/system-overview.md b/docs/architecture/system-overview.md
index 28f59ee..a8e6ad8 100644
--- a/docs/architecture/system-overview.md
+++ b/docs/architecture/system-overview.md
@@ -32,3 +32,8 @@
 - User-caused provider failures are terminal for that request.
 - Balance or quota exhaustion removes a key from active rotation.
 - Provider-key state transitions must be audited.
+
+## Web session posture
+- Browser sessions use `Secure`, `HttpOnly`, `SameSite=Strict` cookies.
+- State-changing cookie-authenticated endpoints accept requests only from the configured app/admin origins and require browser `Origin` or `Referer` metadata.
+- The current API posture assumes a same-origin browser client. If cross-site embeds or third-party POST flows are introduced later, add an explicit CSRF token mechanism instead of relaxing the cookie/origin checks.