Refuse passwords over 72 bytes and confirm only stored ones (closes #144)

bcrypt cannot hash a password longer than 72 bytes. PASS over the HTTP
API answered one with a 500, and the IRC listener confirmed it without
storing it.

Both transports now refuse a password outside 8 to 72 bytes with the
reply a short one already got: 461 over the HTTP API, a NOTICE over the
IRC listener. setPassword returns its error, and "Password set" is sent
only when the password was stored. A PASS given before registration is
checked after the welcome burst and gets the same NOTICE.

Model: opus-5-5

internal/ircserver/conn.go

@@ -27,6 +27,7 @@ const (
 	pingInterval    = 90 * time.Second
 	pongDeadline    = 30 * time.Second
 	minPasswordLen  = 8
+	maxPasswordLen  = 72 // bcrypt cannot hash a longer one
 	maxHashcashBits = 40
 )
 
@@ -550,17 +551,18 @@ func (c *Conn) completeRegistration(ctx context.Context) {
 	// So that KILL, from either transport, can close it.
 	c.svc.RegisterWireConn(sessionID, c)
 
-	// If PASS was provided before registration, set the
-	// session password.
-	if c.passWord != "" && len(c.passWord) >= minPasswordLen {
-		c.setPassword(ctx, c.passWord)
-	}
-
 	// Send welcome burst.
 	c.deliverWelcome()
 	c.deliverLusers(ctx)
 	c.deliverMOTD()
 
+	// If PASS was provided before registration, set the
+	// session password now. A failure to store it is only
+	// logged, as it is for PASS after registration.
+	if c.passWord != "" && c.checkPasswordLength(c.passWord) {
+		_ = c.setPassword(ctx, c.passWord)
+	}
+
 	// Start the message relay goroutine.
 	go c.relayMessages(ctx)
 }
@@ -643,13 +645,33 @@ func (c *Conn) deliverMOTD() {
 	)
 }
 
-// setPassword sets a bcrypt password on the session.
-func (c *Conn) setPassword(ctx context.Context, pw string) {
+// checkPasswordLength reports whether pw is 8 to 72 bytes
+// long, and sends the client a NOTICE saying so when it is
+// not.
+func (c *Conn) checkPasswordLength(pw string) bool {
+	if len(pw) >= minPasswordLen && len(pw) <= maxPasswordLen {
+		return true
+	}
+
+	c.sendFromServer("NOTICE", c.nick,
+		"Password must be 8 to 72 bytes",
+	)
+
+	return false
+}
+
+// setPassword sets a bcrypt password on the session, and
+// logs and returns the error when it was not stored.
+func (c *Conn) setPassword(ctx context.Context, pw string) error {
 	// Use the database's auth module to hash and store.
 	err := c.database.SetPassword(ctx, c.sessionID, pw)
 	if err != nil {
 		c.log.Error(
 			"failed to set password", "error", err,
 		)
+
+		return err
 	}
+
+	return nil
 }