diff --git a/README.md b/README.md
index a8eb5c59b..c6d9da94b 100644
--- a/README.md
+++ b/README.md
@@ -52,12 +52,12 @@ Or get the latest APK from the [Releases Section](https://github.com/vitorpamplo
 - [x] External Identity Support (NIP-39)
 - [x] Multiple Accounts
 - [x] Markdown Support
+- [x] Relay Authentication (NIP-42)
 - [ ] Local Database 
 - [ ] View Individual Reactions (Like, Boost, Zaps, Reports) per Post
 - [ ] Bookmarks, Pinned Posts, Muted Events (NIP-51)
 - [ ] Sensitive Content (NIP-36) 
 - [ ] Relay Pages (NIP-11)
-- [ ] Relay Authentication (NIP-42)
 - [ ] Generic Tags (NIP-12)
 - [ ] Proof of Work in the Phone (NIP-13, NIP-20)
 - [ ] Events with a Subject (NIP-14)
diff --git a/app/src/main/java/com/vitorpamplona/amethyst/model/Account.kt b/app/src/main/java/com/vitorpamplona/amethyst/model/Account.kt
index c81f0c970..e09112dae 100644
--- a/app/src/main/java/com/vitorpamplona/amethyst/model/Account.kt
+++ b/app/src/main/java/com/vitorpamplona/amethyst/model/Account.kt
@@ -569,6 +569,12 @@ class Account(
         LocalCache.consume(event)
     }
 
+    fun createAuthEvent(relay: Relay, challenge: String): RelayAuthEvent? {
+        if (!isWriteable()) return null
+
+        return RelayAuthEvent.create(relay.url, challenge, loggedIn.privKey!!)
+    }
+
     fun removePublicBookmark(note: Note) {
         if (!isWriteable()) return
 
diff --git a/app/src/main/java/com/vitorpamplona/amethyst/service/NostrAccountDataSource.kt b/app/src/main/java/com/vitorpamplona/amethyst/service/NostrAccountDataSource.kt
index a3546f003..3025a742f 100644
--- a/app/src/main/java/com/vitorpamplona/amethyst/service/NostrAccountDataSource.kt
+++ b/app/src/main/java/com/vitorpamplona/amethyst/service/NostrAccountDataSource.kt
@@ -14,8 +14,10 @@ import com.vitorpamplona.amethyst.service.model.ReportEvent
 import com.vitorpamplona.amethyst.service.model.RepostEvent
 import com.vitorpamplona.amethyst.service.model.TextNoteEvent
 import com.vitorpamplona.amethyst.service.relays.COMMON_FEED_TYPES
+import com.vitorpamplona.amethyst.service.relays.Client
 import com.vitorpamplona.amethyst.service.relays.EOSEAccount
 import com.vitorpamplona.amethyst.service.relays.JsonFilter
+import com.vitorpamplona.amethyst.service.relays.Relay
 import com.vitorpamplona.amethyst.service.relays.TypedFilter
 
 object NostrAccountDataSource : NostrDataSource("AccountData") {
@@ -113,4 +115,19 @@ object NostrAccountDataSource : NostrDataSource("AccountData") {
             createAccountBookmarkListFilter()
         ).ifEmpty { null }
     }
+
+    override fun auth(relay: Relay, challenge: String) {
+        super.auth(relay, challenge)
+
+        if (this::account.isInitialized) {
+            val event = account.createAuthEvent(relay, challenge)
+
+            if (event != null) {
+                Client.send(
+                    event,
+                    relay.url
+                )
+            }
+        }
+    }
 }
diff --git a/app/src/main/java/com/vitorpamplona/amethyst/service/NostrDataSource.kt b/app/src/main/java/com/vitorpamplona/amethyst/service/NostrDataSource.kt
index 206a6538a..bdabd984f 100644
--- a/app/src/main/java/com/vitorpamplona/amethyst/service/NostrDataSource.kt
+++ b/app/src/main/java/com/vitorpamplona/amethyst/service/NostrDataSource.kt
@@ -126,6 +126,10 @@ abstract class NostrDataSource(val debugName: String) {
 
         override fun onSendResponse(eventId: String, success: Boolean, message: String, relay: Relay) {
         }
+
+        override fun onAuth(relay: Relay, challenge: String) {
+            auth(relay, challenge)
+        }
     }
 
     init {
@@ -221,4 +225,5 @@ abstract class NostrDataSource(val debugName: String) {
     }
 
     abstract fun updateChannelFilters()
+    open fun auth(relay: Relay, challenge: String) = Unit
 }
diff --git a/app/src/main/java/com/vitorpamplona/amethyst/service/model/RelayAuthEvent.kt b/app/src/main/java/com/vitorpamplona/amethyst/service/model/RelayAuthEvent.kt
new file mode 100644
index 000000000..6a7e04228
--- /dev/null
+++ b/app/src/main/java/com/vitorpamplona/amethyst/service/model/RelayAuthEvent.kt
@@ -0,0 +1,34 @@
+package com.vitorpamplona.amethyst.service.model
+
+import com.vitorpamplona.amethyst.model.HexKey
+import com.vitorpamplona.amethyst.model.toHexKey
+import nostr.postr.Utils
+import java.util.Date
+
+class RelayAuthEvent(
+    id: HexKey,
+    pubKey: HexKey,
+    createdAt: Long,
+    tags: List<List<String>>,
+    content: String,
+    sig: HexKey
+) : Event(id, pubKey, createdAt, kind, tags, content, sig) {
+    fun relay() = tags.firstOrNull() { it.size > 1 && it[0] == "relay" }?.get(1)
+    fun challenge() = tags.firstOrNull() { it.size > 1 && it[0] == "challenge" }?.get(1)
+
+    companion object {
+        const val kind = 22242
+
+        fun create(relay: String, challenge: String, privateKey: ByteArray, createdAt: Long = Date().time / 1000): RelayAuthEvent {
+            val content = ""
+            val pubKey = Utils.pubkeyCreate(privateKey).toHexKey()
+            val tags = listOf(
+                listOf("relay", relay),
+                listOf("challenge", challenge)
+            )
+            val id = generateId(pubKey, createdAt, kind, tags, content)
+            val sig = Utils.sign(id, privateKey)
+            return RelayAuthEvent(id.toHexKey(), pubKey, createdAt, tags, content, sig.toHexKey())
+        }
+    }
+}
diff --git a/app/src/main/java/com/vitorpamplona/amethyst/service/relays/Client.kt b/app/src/main/java/com/vitorpamplona/amethyst/service/relays/Client.kt
index f5631b27e..256e1b804 100644
--- a/app/src/main/java/com/vitorpamplona/amethyst/service/relays/Client.kt
+++ b/app/src/main/java/com/vitorpamplona/amethyst/service/relays/Client.kt
@@ -160,6 +160,14 @@ object Client : RelayPool.Listener {
         }
     }
 
+    override fun onAuth(relay: Relay, challenge: String) {
+        // Releases the Web thread for the new payload.
+        // May need to add a processing queue if processing new events become too costly.
+        GlobalScope.launch(Dispatchers.Default) {
+            listeners.forEach { it.onAuth(relay, challenge) }
+        }
+    }
+
     fun subscribe(listener: Listener) {
         listeners = listeners.plus(listener)
     }
@@ -196,5 +204,7 @@ object Client : RelayPool.Listener {
          * When an relay saves or rejects a new event.
          */
         open fun onSendResponse(eventId: String, success: Boolean, message: String, relay: Relay) = Unit
+
+        open fun onAuth(relay: Relay, challenge: String) = Unit
     }
 }
diff --git a/app/src/main/java/com/vitorpamplona/amethyst/service/relays/Relay.kt b/app/src/main/java/com/vitorpamplona/amethyst/service/relays/Relay.kt
index 21928f64a..68137cd57 100644
--- a/app/src/main/java/com/vitorpamplona/amethyst/service/relays/Relay.kt
+++ b/app/src/main/java/com/vitorpamplona/amethyst/service/relays/Relay.kt
@@ -122,6 +122,10 @@ class Relay(
                                 // Log.w("Relay", "Relay on OK $url, $channel")
                                 it.onSendResponse(this@Relay, msg[1].asString, msg[2].asBoolean, msg[3].asString)
                             }
+                            "AUTH" -> listeners.forEach {
+                                // Log.w("Relay", "Relay AUTH $url, $channel")
+                                it.onAuth(this@Relay, msg[1].asString)
+                            }
                             else -> listeners.forEach {
                                 // Log.w("Relay", "Relay something else $url, $channel")
                                 it.onError(
@@ -272,6 +276,8 @@ class Relay(
 
         fun onSendResponse(relay: Relay, eventId: String, success: Boolean, message: String)
 
+        fun onAuth(relay: Relay, challenge: String)
+
         /**
          * Connected to or disconnected from a relay
          *
diff --git a/app/src/main/java/com/vitorpamplona/amethyst/service/relays/RelayPool.kt b/app/src/main/java/com/vitorpamplona/amethyst/service/relays/RelayPool.kt
index e1d5bb215..702bdc1b2 100644
--- a/app/src/main/java/com/vitorpamplona/amethyst/service/relays/RelayPool.kt
+++ b/app/src/main/java/com/vitorpamplona/amethyst/service/relays/RelayPool.kt
@@ -93,6 +93,8 @@ object RelayPool : Relay.Listener {
         fun onRelayStateChange(type: Relay.Type, relay: Relay, channel: String?)
 
         fun onSendResponse(eventId: String, success: Boolean, message: String, relay: Relay)
+
+        fun onAuth(relay: Relay, challenge: String)
     }
 
     override fun onEvent(relay: Relay, subscriptionId: String, event: Event) {
@@ -113,6 +115,10 @@ object RelayPool : Relay.Listener {
         listeners.forEach { it.onSendResponse(eventId, success, message, relay) }
     }
 
+    override fun onAuth(relay: Relay, challenge: String) {
+        listeners.forEach { it.onAuth(relay, challenge) }
+    }
+
     // Observers line up here.
     val live: RelayPoolLiveData = RelayPoolLiveData(this)