diff --git a/crates/projection-irc/src/lib.rs b/crates/projection-irc/src/lib.rs
index 82c3d29..ff3d892 100644
--- a/crates/projection-irc/src/lib.rs
+++ b/crates/projection-irc/src/lib.rs
@@ -181,19 +181,15 @@ async fn handle_registration<'a>(
                 }
                 CapabilitySubcommand::End => {
                     let Some((ref username, ref realname)) = future_username else {
-                        sasl_fail_message(config.server_name.clone()).write_async(writer).await?;
-                        writer.flush().await?;
-                        continue;
+                        break Err(anyhow::Error::msg("Protocol violated"));
                     };
                     let Some(nickname) = future_nickname.clone() else {
-                        sasl_fail_message(config.server_name.clone()).write_async(writer).await?;
-                        writer.flush().await?;
-                        continue;
+                        break Err(anyhow::Error::msg("Protocol violated"));
                     };
                     let username = username.clone();
                     let realname = realname.clone();
                     let candidate_user = RegisteredUser {
-                        nickname,
+                        nickname: nickname.clone(),
                         username,
                         realname
                     };
@@ -203,7 +199,11 @@ async fn handle_registration<'a>(
                         break Ok(candidate_user);
                     } else {
                         let Some(candidate_password) = pass else {
-                            sasl_fail_message(config.server_name.clone()).write_async(writer).await?;
+                            sasl_fail_message(
+                                config.server_name.clone(), 
+                                nickname.clone(), 
+                                "User credentials was not provided".into()
+                            ).write_async(writer).await?;
                             writer.flush().await?;
                             continue;
                         };
@@ -217,12 +217,16 @@ async fn handle_registration<'a>(
                     future_nickname = Some(nickname);
                 } else if let Some((username, realname)) = future_username.clone() {
                     let candidate_user = RegisteredUser {
-                        nickname,
+                        nickname: nickname.clone(),
                         username,
                         realname,
                     };
                     let Some(candidate_password) = pass else {
-                        sasl_fail_message(config.server_name.clone()).write_async(writer).await?;
+                        sasl_fail_message(
+                            config.server_name.clone(), 
+                            nickname.clone(), 
+                            "User credentials was not provided".into()
+                        ).write_async(writer).await?;
                         writer.flush().await?;
                         continue;
                     };
@@ -237,12 +241,16 @@ async fn handle_registration<'a>(
                     future_username = Some((username, realname));
                 } else if let Some(nickname) = future_nickname.clone() {
                     let candidate_user = RegisteredUser {
-                        nickname,
+                        nickname: nickname.clone(),
                         username,
                         realname,
                     };
                     let Some(candidate_password) = pass else {
-                        sasl_fail_message(config.server_name.clone()).write_async(writer).await?;
+                        sasl_fail_message(
+                            config.server_name.clone(), 
+                            nickname.clone(), 
+                            "User credentials was not provided".into()
+                        ).write_async(writer).await?;
                         writer.flush().await?;
                         continue;
                     };
@@ -267,46 +275,52 @@ async fn handle_registration<'a>(
                         .await?;
                         writer.flush().await?;
                     } else {
-                        sasl_fail_message(config.server_name.clone()).write_async(writer).await?;
-                        writer.flush().await?;
+                        if let Some(nickname) = future_nickname.clone() {
+                            sasl_fail_message(config.server_name.clone(), nickname.clone(), "Unsupported mechanism".into()).write_async(writer).await?;
+                            writer.flush().await?;
+                        } else {
+                            break Err(anyhow::Error::msg("Wrong authentication sequence"));
+                        }
                     }
                 } else {
                     let body = AuthBody::from_str(body.as_bytes())?;
-                    match auth_user(storage, &body.login, &body.password).await {
-                        Err(e) => {
-                            tracing::warn!("Authentication failed: {:?}", e);
-                            sasl_fail_message(config.server_name.clone()).write_async(writer).await?;
+                    if let Err(e) = auth_user(storage, &body.login, &body.password).await {
+                        tracing::warn!("Authentication failed: {:?}", e);
+                        if let Some(nickname) = future_nickname.clone() {
+                            sasl_fail_message(config.server_name.clone(), nickname.clone(), "Bad credentials".into()).write_async(writer).await?;
                             writer.flush().await?;
+                        } else {
+
                         }
-                        Ok(_) => {
-                            let login: Str = body.login.into();
-                            validated_user = Some(login.clone());
-                            ServerMessage {
-                                tags: vec![],
-                                sender: Some(config.server_name.clone().into()),
-                                body: ServerMessageBody::N900LoggedIn {
-                                    nick: login.clone(),
-                                    address: login.clone(),
-                                    account: login.clone(),
-                                    message: format!("You are now logged in as {}", login).into(),
-                                },
-                            }
-                            .write_async(writer)
-                            .await?;
-                            ServerMessage {
-                                tags: vec![],
-                                sender: Some(config.server_name.clone().into()),
-                                body: ServerMessageBody::N903SaslSuccess {
-                                    nick: login.clone(),
-                                    message: "SASL authentication successful".into(),
-                                },
-                            }
-                            .write_async(writer)
-                            .await?;
-                            writer.flush().await?;
+                    } else {
+                        let login: Str = body.login.into();
+                        validated_user = Some(login.clone());
+                        ServerMessage {
+                            tags: vec![],
+                            sender: Some(config.server_name.clone().into()),
+                            body: ServerMessageBody::N900LoggedIn {
+                                nick: login.clone(),
+                                address: login.clone(),
+                                account: login.clone(),
+                                message: format!("You are now logged in as {}", login).into(),
+                            },
                         }
+                        .write_async(writer)
+                        .await?;
+                        ServerMessage {
+                            tags: vec![],
+                            sender: Some(config.server_name.clone().into()),
+                            body: ServerMessageBody::N903SaslSuccess {
+                                nick: login.clone(),
+                                message: "SASL authentication successful".into(),
+                            },
+                        }
+                        .write_async(writer)
+                        .await?;
+                        writer.flush().await?;
                     }
                 }
+                
                 // TODO handle abortion of authentication
             }
             _ => {}
@@ -317,11 +331,11 @@ async fn handle_registration<'a>(
     Ok(user)
 }
 
-fn sasl_fail_message(sender: Str) -> ServerMessage {
+fn sasl_fail_message(sender: Str, nick: Str, text: Str) -> ServerMessage {
     ServerMessage {
         tags: vec![],
         sender: Some(sender),
-        body: ServerMessageBody::N904SaslFail
+        body: ServerMessageBody::N904SaslFail { nick, text }
     }
 }
 
diff --git a/crates/projection-irc/tests/lib.rs b/crates/projection-irc/tests/lib.rs
index 7ddf427..1a686a4 100644
--- a/crates/projection-irc/tests/lib.rs
+++ b/crates/projection-irc/tests/lib.rs
@@ -241,6 +241,8 @@ async fn scenario_cap_sasl_fail() -> Result<()> {
     s.expect(":testserver 904").await?;
     s.send("AUTHENTICATE PLAIN").await?;
     s.expect(":testserver AUTHENTICATE +").await?;
+    s.send("AUTHENTICATE wrong_password").await?;
+    s.expect(":testserver 904").await?;
     s.send("AUTHENTICATE dGVzdGVyAHRlc3RlcgBwYXNzd29yZA==").await?; // base64-encoded 'tester\x00tester\x00password'
     s.expect(":testserver 900 tester tester tester :You are now logged in as tester").await?;
     s.expect(":testserver 903 tester :SASL authentication successful").await?;
diff --git a/crates/proto-irc/src/server.rs b/crates/proto-irc/src/server.rs
index aff864d..4c1836c 100644
--- a/crates/proto-irc/src/server.rs
+++ b/crates/proto-irc/src/server.rs
@@ -161,7 +161,10 @@ pub enum ServerMessageBody {
         nick: Str,
         message: Str,
     },
-    N904SaslFail
+    N904SaslFail {
+        nick: Str,
+        text: Str,
+    }
 }
 
 impl ServerMessageBody {
@@ -393,8 +396,12 @@ impl ServerMessageBody {
                 writer.write_all(b" :").await?;
                 writer.write_all(message.as_bytes()).await?;
             }
-            ServerMessageBody::N904SaslFail => {
+            ServerMessageBody::N904SaslFail { nick, text } => {
                 writer.write_all(b"904").await?;
+                writer.write_all(b" ").await?;
+                writer.write_all(nick.as_bytes()).await?;
+                writer.write_all(b" :").await?;
+                writer.write_all(text.as_bytes()).await?;
             }
         }
         Ok(())