Handle mysql_old_password consistently.

A NotSupportedException will still be thrown, but with a more helpful exception message.

An old-style Authentication Method Switch Request (single byte packet) will be implicitly converted to a request for 'mysql_old_password'.

Author: bgrainger

src/MySqlConnector/Serialization/AuthenticationMethodSwitchRequestPayload.cs

@@ -1,4 +1,4 @@
-using System.Text;
+using System.Text;
 
 namespace MySql.Data.Serialization
 {
@@ -13,8 +13,20 @@ public static AuthenticationMethodSwitchRequestPayload Create(PayloadData payloa
 		{
 			var reader = new ByteArrayReader(payload.ArraySegment);
 			reader.ReadByte(Signature);
-			var name = Encoding.UTF8.GetString(reader.ReadNullTerminatedByteString());
-			var data = reader.ReadByteString(reader.BytesRemaining);
+			string name;
+			byte[] data;
+			if (payload.ArraySegment.Count == 1)
+			{
+				// if the packet is just the header byte (0xFE), it's an "Old Authentication Method Switch Request Packet"
+				// (possibly sent by a server that doesn't support CLIENT_PLUGIN_AUTH)
+				name = "mysql_old_password";
+				data = new byte[0];
+			}
+			else
+			{
+				name = Encoding.UTF8.GetString(reader.ReadNullTerminatedByteString());
+				data = reader.ReadByteString(reader.BytesRemaining);
+			}
 			return new AuthenticationMethodSwitchRequestPayload(name, data);
 		}
 

src/MySqlConnector/Serialization/MySqlSession.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Diagnostics;
 using System.Globalization;
 using System.IO;
@@ -242,18 +242,8 @@ public async Task ConnectAsync(ConnectionSettings cs, IOBehavior ioBehavior, Can
 			// if server doesn't support the authentication fast path, it will send a new challenge
 			if (payload.HeaderByte == AuthenticationMethodSwitchRequestPayload.Signature)
 			{
-				if (payload.ArraySegment.Count == 1)
-				{
-					// Single 0xfe byte of the payload means it's an Old Authentication Method Switch Request Packet.
-					// See http://imysql.com/mysql-internal-manual/connection-phase-packets.html
-					// It's old protocol so MySqlConnector doesn't support it.
-					throw new NotSupportedException("Old Authentication Method Switch is not supported. Use new password hash format of 41-byte in MySQL server, not old format of 16-byte.");
-				}
-				else
-				{
-					await SwitchAuthenticationAsync(cs, payload, ioBehavior, cancellationToken).ConfigureAwait(false);
-					payload = await ReceiveReplyAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
-				}
+				await SwitchAuthenticationAsync(cs, payload, ioBehavior, cancellationToken).ConfigureAwait(false);
+				payload = await ReceiveReplyAsync(ioBehavior, cancellationToken).ConfigureAwait(false);
 			}
 
 			OkPayload.Create(payload);
@@ -381,6 +371,9 @@ private async Task SwitchAuthenticationAsync(ConnectionSettings cs, PayloadData
 				}
 				break;
 
+			case "mysql_old_password":
+				throw new NotSupportedException("'MySQL Server is requesting the insecure pre-4.1 auth mechanism (mysql_old_password). The user password must be upgraded; see https://dev.mysql.com/doc/refman/5.7/en/account-upgrades.html.");
+
 			default:
 				throw new NotSupportedException("Authentication method '{0}' is not supported.".FormatInvariant(switchRequest.Name));
 			}