feat(smtp): add AUTH LOGIN support

- support servers that offer LOGIN without other mechanisms
- encode username and password as base64 prompt responses
- restrict LOGIN authentication to secured connections
- mark the connection authenticated after a successful exchange

1 files changed, 41 insertions, 0 deletions

diff --git a/src/vmime/net/smtp/SMTPConnection.cpp b/src/vmime/net/smtp/SMTPConnection.cpp
index 07d03765..e7620f79 100644
--- a/src/vmime/net/smtp/SMTPConnection.cpp
+++ b/src/vmime/net/smtp/SMTPConnection.cpp
@@ -359,6 +359,47 @@ void SMTPConnection::authenticate() {
 				return;
 			}
 		}
+
+		// AUTH LOGIN, for the many servers that offer it and nothing else we
+		// can speak. Without SASL, PLAIN alone leaves those servers
+		// unreachable. Still inside the m_secured guard above: LOGIN sends the
+		// username and password as bare base64, which is encoding and not
+		// encryption, so it must never touch a cleartext socket.
+		const string login("LOGIN");
+
+		if (std::find(authMechs.begin(), authMechs.end(), login) != authMechs.end()) {
+
+			const string username = getAuthenticator()->getUsername();
+			const string password = getAuthenticator()->getPassword();
+
+			// LOGIN is a three-step conversation: the server prompts for each
+			// field with a 334 and we answer with one base64 line.
+			const auto sendBase64 = [&](const string& value) -> int {
+				utility::inputStreamStringAdapter in(value);
+				string encoded;
+				utility::outputStreamStringAdapter out(encoded);
+
+				vmime::utility::encoder::b64Encoder encoder;
+				encoder.encode(in, out);
+
+				m_socket->send(encoded + "\r\n");
+
+				shared_ptr <SMTPResponse> resp = readResponse();
+				return resp ? resp->getCode() : -1;
+			};
+
+			sendRequest(SMTPCommand::AUTH(login));
+
+			shared_ptr <SMTPResponse> response = readResponse();
+
+			if (response && response->getCode() == 334) {
+
+				if (sendBase64(username) == 334 && sendBase64(password) == 235) {
+					m_authenticated = true;
+					return;
+				}
+			}
+		}
 	}
 
 #endif // VMIME_HAVE_SASL_SUPPORT