Error when invoking Authenticate multiple times over the same connection

[Eitan Behar]

Describe the bug
Calling client.Authenticate(credentials.username, credentials.password); twice with the same or different credentials
returns error System.InvalidOperationException: The SmtpClient is already authenticated.

Platform (please complete the following information):

• OS: MacOS
• .NET Runtime: 6.0
• .NET Framework: 6.0
• MailKit Version: MailKit, 2.15.0 - HttpToSocks5Proxy, 1.4.0

Exception
Error: System.InvalidOperationException: The SmtpClient is already authenticated.
at MailKit.Net.Smtp.SmtpClient.AuthenticateAsync(Encoding encoding, ICredentials credentials, Boolean doAsync, CancellationToken cancellationToken) in D:\src\MailKit\MailKit\Net\Smtp\SmtpClient.cs:line 886
at MailKit.Net.Smtp.SmtpClient.Authenticate(Encoding encoding, ICredentials credentials, CancellationToken cancellationToken) in D:\src\MailKit\MailKit\Net\Smtp\SmtpClient.cs:line 1027
at MailKit.MailService.Authenticate(Encoding encoding, String userName, String password, CancellationToken cancellationToken) in D:\src\MailKit\MailKit\MailService.cs:line 1326
at MailKit.MailService.Authenticate(String userName, String password, CancellationToken cancellationToken) in D:\src\MailKit\MailKit\MailService.cs:line 1442
at Submission#4.SendUsingMailKitProxy(MimeMessage message, String smtpUrl, String proxyUrl, Credentials credentials)
at Submission#4.<>d__0.MoveNext()
--- End of stack trace from previous location ---

To Reproduce
Steps to reproduce the behavior:
Connect and Authorize twice
4. See error

Expected behavior
Further authentication should do a new authentication over the existing connection
or, there should be a way to -deauthenticate without disconnecting

Code Snippets
If applicable, add code snippets to help explain your problem.

var client = new MailKit.Net.Smtp.SmtpClient()
var proxy = new HttpProxyClient(Url, Port);
client.ServerCertificateValidationCallback = (s, c, h, e) => true;
client.ProxyClient = proxy;
client.Connect(smtpUrl, smtpPort, SecureSocketOptions.StartTls);
client.Authenticate(credentials.username, credentials.password);
client.Authenticate(credentials.username, credentials.password);

Protocol Logs
Please include a protocol log (scrubbed of any authentication data), especially
if you got an exception such as Syntax error in XYZ. Unexpected token: ....

To get a protocol log, follow one of the following code snippets:

// log to a file called 'imap.log'
var client = new ImapClient (new ProtocolLogger ("imap.log"));

// log to a file called 'pop3.log'
var client = new Pop3Client (new ProtocolLogger ("pop3.log"));

// log to a file called 'smtp.log'
var client = new SmtpClient (new ProtocolLogger ("smtp.log"));

Note: if the protocol log contains sensitive information, feel free to email it to me at
[e-mail] instead of including it in the GitHub issue.

Additional context
Add any other context about the problem here.

[Jeffrey Stedfast]

There's no way to do what you want. The SMTP protocol does not support un-authenticating or re-authenticating with a new account/password.

The only way is to disconnect and then connect/authenticate as far as I'm aware.