Mail: client SSL certificates support. The "ssl_verify_client", "ssl_verify_depth", "ssl_client_certificate", "ssl_trusted_certificate", and "ssl_crl" directives introduced to control SSL client certificate verification in mail proxy module. If there is a certificate, detail of the certificate are passed to the auth_http script configured via Auth-SSL-Verify, Auth-SSL-Subject, Auth-SSL-Issuer, Auth-SSL-Serial, Auth-SSL-Fingerprint headers. If the auth_http_pass_client_cert directive is set, client certificate in PEM format will be passed in the Auth-SSL-Cert header (urlencoded). If there is no required certificate provided during an SSL handshake or certificate verification fails then a protocol-specific error is returned after the SSL handshake and the connection is closed. Based on previous work by Sven Peter, Franck Levionnois and Filipe Da Silva.

--- a/src/mail/ngx_mail_imap_module.c
+++ b/src/mail/ngx_mail_imap_module.c
@@ -52,7 +52,9 @@ static ngx_mail_protocol_t  ngx_mail_ima
     ngx_mail_imap_parse_command,
     ngx_mail_imap_auth_state,
 
-    ngx_string("* BAD internal server error" CRLF)
+    ngx_string("* BAD internal server error" CRLF),
+    ngx_string("* BYE SSL certificate error" CRLF),
+    ngx_string("* BYE No required SSL certificate" CRLF)
 };