diff --git a/src/app.ts b/src/app.ts
index 0fe0b62b..9104e2bb 100644
--- a/src/app.ts
+++ b/src/app.ts
@@ -1,4 +1,5 @@
 import { type Context, cors, type Handler, Hono, type HonoEnv, logger, type MiddlewareHandler } from '@/deps.ts';
+import { type Event } from '@/event.ts';
 
 import {
   accountController,
@@ -26,7 +27,8 @@ import {
 } from './controllers/api/statuses.ts';
 import { streamingController } from './controllers/api/streaming.ts';
 import { indexController } from './controllers/site.ts';
-import { requireAuth, setAuth } from './middleware/auth.ts';
+import { auth19, requireAuth } from './middleware/auth19.ts';
+import { auth98 } from './middleware/auth98.ts';
 
 interface AppEnv extends HonoEnv {
   Variables: {
@@ -36,6 +38,8 @@ interface AppEnv extends HonoEnv {
     seckey?: string;
     /** UUID from the access token. Used for WebSocket event signing. */
     session?: string;
+    /** NIP-98 signed event proving the pubkey is owned by the user. */
+    proof?: Event<27235>;
   };
 }
 
@@ -50,7 +54,7 @@ app.use('*', logger());
 app.get('/api/v1/streaming', streamingController);
 app.get('/api/v1/streaming/', streamingController);
 
-app.use('*', cors({ origin: '*', exposeHeaders: ['link'] }), setAuth);
+app.use('*', cors({ origin: '*', exposeHeaders: ['link'] }), auth19, auth98());
 
 app.get('/api/v1/instance', instanceController);
 
diff --git a/src/controllers/api/streaming.ts b/src/controllers/api/streaming.ts
index b99000cf..412e0240 100644
--- a/src/controllers/api/streaming.ts
+++ b/src/controllers/api/streaming.ts
@@ -1,5 +1,5 @@
 import { AppController } from '@/app.ts';
-import { TOKEN_REGEX } from '@/middleware/auth.ts';
+import { TOKEN_REGEX } from '@/middleware/auth19.ts';
 import { streamSchema, ws } from '@/stream.ts';
 import { bech32ToPubkey } from '@/utils.ts';
 
diff --git a/src/middleware/auth.ts b/src/middleware/auth19.ts
similarity index 89%
rename from src/middleware/auth.ts
rename to src/middleware/auth19.ts
index 358c5bd5..46f125f9 100644
--- a/src/middleware/auth.ts
+++ b/src/middleware/auth19.ts
@@ -1,4 +1,4 @@
-import { AppMiddleware } from '@/app.ts';
+import { type AppMiddleware } from '@/app.ts';
 import { getPublicKey, HTTPException, nip19 } from '@/deps.ts';
 
 /** The token includes a Bech32 Nostr ID (npub, nsec, etc) and an optional session ID. */
@@ -7,7 +7,7 @@ const TOKEN_REGEX = new RegExp(`(${nip19.BECH32_REGEX.source})(?:_(\\w+))?`);
 const BEARER_REGEX = new RegExp(`^Bearer (${TOKEN_REGEX.source})$`);
 
 /** NIP-19 auth middleware. */
-const setAuth: AppMiddleware = async (c, next) => {
+const auth19: AppMiddleware = async (c, next) => {
   const authHeader = c.req.headers.get('authorization');
   const match = authHeader?.match(BEARER_REGEX);
 
@@ -47,4 +47,4 @@ const requireAuth: AppMiddleware = async (c, next) => {
   await next();
 };
 
-export { requireAuth, setAuth, TOKEN_REGEX };
+export { auth19, requireAuth, TOKEN_REGEX };
diff --git a/src/middleware/auth98.ts b/src/middleware/auth98.ts
new file mode 100644
index 00000000..4910b0ed
--- /dev/null
+++ b/src/middleware/auth98.ts
@@ -0,0 +1,74 @@
+import { type AppMiddleware } from '@/app.ts';
+import { Conf } from '@/config.ts';
+import { HTTPException } from '@/deps.ts';
+import { type Event } from '@/event.ts';
+import { decode64Schema, jsonSchema, signedEventSchema } from '@/schema.ts';
+import { eventAge, findTag, sha256, Time } from '@/utils.ts';
+
+const decodeEventSchema = decode64Schema.pipe(jsonSchema).pipe(signedEventSchema);
+
+interface Auth98Opts {
+  timeout?: number;
+}
+
+/**
+ * NIP-98 auth.
+ * https://github.com/nostr-protocol/nips/blob/master/98.md
+ */
+function auth98(opts: Auth98Opts = {}): AppMiddleware {
+  return async (c, next) => {
+    const authHeader = c.req.headers.get('authorization');
+    const base64 = authHeader?.match(/^Nostr (.+)$/)?.[1];
+    const { timeout = Time.minutes(1) } = opts;
+
+    const schema = decodeEventSchema
+      .refine((event) => event.kind === 27235)
+      .refine((event) => eventAge(event) < timeout)
+      .refine((event) => findTag(event.tags, 'method')?.[1] === c.req.method)
+      .refine((event) => {
+        const url = findTag(event.tags, 'u')?.[1];
+        try {
+          return url === localUrl(c.req.url);
+        } catch (_e) {
+          return false;
+        }
+      })
+      .refine(async (event) => {
+        const body = await c.req.raw.clone().text();
+        if (!body) return true;
+        const hash = findTag(event.tags, 'payload')?.[1];
+        return hash === await sha256(body);
+      });
+
+    const result = await schema.safeParseAsync(base64);
+
+    if (result.success) {
+      c.set('pubkey', result.data.pubkey);
+      c.set('proof', result.data as Event<27235>);
+    }
+
+    await next();
+  };
+}
+
+function localUrl(url: string): string {
+  const { pathname } = new URL(url);
+  return new URL(pathname, Conf.localDomain).toString();
+}
+
+const requireProof: AppMiddleware = async (c, next) => {
+  const pubkey = c.get('pubkey');
+  const proof = c.get('proof');
+
+  // if (!proof && hasWebsocket(c.req)) {
+  //   // TODO: attempt to sign nip98 event through websocket
+  // }
+
+  if (!pubkey || !proof || proof.pubkey !== pubkey) {
+    throw new HTTPException(401);
+  }
+
+  await next();
+};
+
+export { auth98, requireProof };
diff --git a/src/schema.ts b/src/schema.ts
index 53febf5a..9af967e7 100644
--- a/src/schema.ts
+++ b/src/schema.ts
@@ -17,7 +17,7 @@ function filteredArray<T extends z.ZodTypeAny>(schema: T) {
 
 const jsonSchema = z.string().transform((value, ctx) => {
   try {
-    return JSON.parse(value);
+    return JSON.parse(value) as unknown;
   } catch (_e) {
     ctx.addIssue({ code: z.ZodIssueCode.custom, message: 'Invalid JSON' });
     return z.NEVER;
@@ -77,13 +77,27 @@ const eventSchema = z.object({
   created_at: z.number(),
   pubkey: nostrIdSchema,
   sig: z.string(),
-}).refine(verifySignature);
+});
+
+const signedEventSchema = eventSchema.refine(verifySignature);
 
 const emojiTagSchema = z.tuple([z.literal('emoji'), z.string(), z.string().url()]);
 
+/** https://developer.mozilla.org/en-US/docs/Glossary/Base64#the_unicode_problem */
+const decode64Schema = z.string().transform((value, ctx) => {
+  try {
+    const binString = atob(value);
+    const bytes = Uint8Array.from(binString, (m) => m.codePointAt(0)!);
+    return new TextDecoder().decode(bytes);
+  } catch (_e) {
+    ctx.addIssue({ code: z.ZodIssueCode.custom, message: 'Invalid base64' });
+    return z.NEVER;
+  }
+});
+
 export {
+  decode64Schema,
   emojiTagSchema,
-  eventSchema,
   filteredArray,
   jsonSchema,
   type MetaContent,
@@ -91,4 +105,5 @@ export {
   parseMetaContent,
   parseRelay,
   relaySchema,
+  signedEventSchema,
 };
diff --git a/src/sign.ts b/src/sign.ts
index f222e11d..228496f7 100644
--- a/src/sign.ts
+++ b/src/sign.ts
@@ -1,6 +1,6 @@
 import { type AppContext } from '@/app.ts';
 import { getEventHash, getPublicKey, getSignature, HTTPException, z } from '@/deps.ts';
-import { eventSchema } from '@/schema.ts';
+import { signedEventSchema } from '@/schema.ts';
 import { ws } from '@/stream.ts';
 
 import type { Event, EventTemplate, SignedEvent } from '@/event.ts';
@@ -18,7 +18,7 @@ function getSignStream(c: AppContext): WebSocket | undefined {
 
 const nostrStreamingEventSchema = z.object({
   type: z.literal('nostr.sign'),
-  data: eventSchema,
+  data: signedEventSchema,
 });
 
 /**
diff --git a/src/utils.ts b/src/utils.ts
index c78e1cf7..191d5e72 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -101,10 +101,46 @@ function buildLinkHeader(url: string, events: Event[]): string | undefined {
   return `<${next}>; rel="next", <${prev}>; rel="prev"`;
 }
 
+/** Return the event's age in milliseconds. */
+function eventAge(event: Event): number {
+  return new Date().getTime() - nostrDate(event.created_at).getTime();
+}
+
+const Time = {
+  milliseconds: (ms: number) => ms,
+  seconds: (s: number) => s * 1000,
+  minutes: (m: number) => m * Time.seconds(60),
+  hours: (h: number) => h * Time.minutes(60),
+  days: (d: number) => d * Time.hours(24),
+  weeks: (w: number) => w * Time.days(7),
+  months: (m: number) => m * Time.days(30),
+  years: (y: number) => y * Time.days(365),
+};
+
+function findTag(tags: string[][], name: string): string[] | undefined {
+  return tags.find((tag) => tag[0] === name);
+}
+
+/**
+ * Get sha256 hash (hex) of some text.
+ * https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto/digest#converting_a_digest_to_a_hex_string
+ */
+async function sha256(message: string): Promise<string> {
+  const msgUint8 = new TextEncoder().encode(message);
+  const hashBuffer = await crypto.subtle.digest('SHA-256', msgUint8);
+  const hashArray = Array.from(new Uint8Array(hashBuffer));
+  const hashHex = hashArray
+    .map((b) => b.toString(16).padStart(2, '0'))
+    .join('');
+  return hashHex;
+}
+
 export {
   bech32ToPubkey,
   buildLinkHeader,
+  eventAge,
   eventDateComparator,
+  findTag,
   lookupAccount,
   type Nip05,
   nostrDate,
@@ -113,4 +149,6 @@ export {
   paginationSchema,
   parseBody,
   parseNip05,
+  sha256,
+  Time,
 };