diff --git a/index.ts b/index.ts
index 8f45843..6fbe9e2 100644
--- a/index.ts
+++ b/index.ts
@@ -13,6 +13,7 @@ export * as nip13 from './nip13'
 export * as nip19 from './nip19'
 export * as nip26 from './nip26'
 export * as nip39 from './nip39'
+export * as nip42 from './nip42'
 export * as nip57 from './nip57'
 
 export * as fj from './fakejson'
diff --git a/nip42.test.js b/nip42.test.js
new file mode 100644
index 0000000..4cedbc8
--- /dev/null
+++ b/nip42.test.js
@@ -0,0 +1,27 @@
+/* eslint-env jest */
+
+require('websocket-polyfill')
+const {
+  relayInit,
+  generatePrivateKey,
+  finishEvent,
+  nip42
+} = require('./lib/nostr.cjs')
+
+test('auth flow', done => {
+  const relay = relayInit('wss://nostr.kollider.xyz')
+  relay.connect()
+  const sk = generatePrivateKey()
+
+  relay.on('auth', async challenge => {
+    await expect(
+      nip42.authenticate({
+        challenge,
+        relay,
+        sign: e => finishEvent(e, sk)
+      })
+    ).rejects.toBeTruthy()
+    relay.close()
+    done()
+  })
+})
diff --git a/nip42.ts b/nip42.ts
new file mode 100644
index 0000000..3df325a
--- /dev/null
+++ b/nip42.ts
@@ -0,0 +1,42 @@
+import {EventTemplate, Event, Kind} from './event'
+import {Relay} from './relay'
+
+/**
+ * Authenticate via NIP-42 flow.
+ *
+ * @example
+ * const sign = window.nostr.signEvent
+ * relay.on('auth', challenge =>
+ *   authenticate({ relay, sign, challenge })
+ * )
+ */
+export const authenticate = async ({
+  challenge,
+  relay,
+  sign
+}: {
+  challenge: string
+  relay: Relay
+  sign: (e: EventTemplate) => Promise<Event>
+}): Promise<void> => {
+  const e: EventTemplate = {
+    kind: Kind.ClientAuth,
+    created_at: Math.floor(Date.now() / 1000),
+    tags: [
+      ['relay', relay.url],
+      ['challenge', challenge]
+    ],
+    content: ''
+  }
+  const sub = relay.publish(await sign(e), 'AUTH')
+  return new Promise((resolve, reject) => {
+    sub.on('ok', function ok() {
+      sub.off('ok', ok)
+      resolve()
+    })
+    sub.on('failed', function fail(reason: string) {
+      sub.off('failed', fail)
+      reject(reason)
+    })
+  })
+}
diff --git a/relay.ts b/relay.ts
index 06dd9ce..68265a4 100644
--- a/relay.ts
+++ b/relay.ts
@@ -4,11 +4,13 @@ import {Event, verifySignature, validateEvent} from './event'
 import {Filter, matchFilters} from './filter'
 import {getHex64, getSubscriptionId} from './fakejson'
 
+type OutgoingEventType = 'EVENT' | 'AUTH'
 type RelayEvent = {
   connect: () => void | Promise<void>
   disconnect: () => void | Promise<void>
   error: () => void | Promise<void>
   notice: (msg: string) => void | Promise<void>
+  auth: (challenge: string) => void | Promise<void>
 }
 type CountPayload = {
   count: number
@@ -26,8 +28,11 @@ export type Relay = {
   sub: (filters: Filter[], opts?: SubscriptionOptions) => Sub
   list: (filters: Filter[], opts?: SubscriptionOptions) => Promise<Event[]>
   get: (filter: Filter, opts?: SubscriptionOptions) => Promise<Event | null>
-  count: (filters: Filter[], opts?: SubscriptionOptions) => Promise<CountPayload | null>
-  publish: (event: Event) => Pub
+  count: (
+    filters: Filter[],
+    opts?: SubscriptionOptions
+  ) => Promise<CountPayload | null>
+  publish: (event: Event, type?: OutgoingEventType) => Pub
   off: <T extends keyof RelayEvent, U extends RelayEvent[T]>(
     event: T,
     listener: U
@@ -61,6 +66,14 @@ export type SubscriptionOptions = {
   alreadyHaveEvent?: null | ((id: string, relay: string) => boolean)
 }
 
+const newListeners = (): {[TK in keyof RelayEvent]: RelayEvent[TK][]} => ({
+  connect: [],
+  disconnect: [],
+  error: [],
+  notice: [],
+  auth: []
+})
+
 export function relayInit(
   url: string,
   options: {
@@ -73,12 +86,7 @@ export function relayInit(
 
   var ws: WebSocket
   var openSubs: {[id: string]: {filters: Filter[]} & SubscriptionOptions} = {}
-  var listeners: {[TK in keyof RelayEvent]: RelayEvent[TK][]} = {
-    connect: [],
-    disconnect: [],
-    error: [],
-    notice: []
-  }
+  var listeners = newListeners()
   var subListeners: {
     [subid: string]: {[TK in keyof SubEvent]: SubEvent[TK][]}
   } = {}
@@ -198,6 +206,11 @@ export function relayInit(
               let notice = data[1]
               listeners.notice.forEach(cb => cb(notice))
               return
+            case 'AUTH': {
+              let challenge = data[1]
+              listeners.auth?.forEach(cb => cb(challenge))
+              return
+            }
           }
         } catch (err) {
           return
@@ -351,11 +364,11 @@ export function relayInit(
           resolve(event)
         })
       }),
-    publish(event: Event): Pub {
+    publish(event, type = 'EVENT'): Pub {
       if (!event.id) throw new Error(`event ${event} has no id`)
       let id = event.id
 
-      trySend(['EVENT', event])
+      trySend([type, event])
 
       return {
         on: (type: 'ok' | 'failed', cb: any) => {
@@ -375,7 +388,7 @@ export function relayInit(
     },
     connect,
     close(): void {
-      listeners = {connect: [], disconnect: [], error: [], notice: []}
+      listeners = newListeners()
       subListeners = {}
       pubListeners = {}
       if (ws.readyState === WebSocket.OPEN) {