Replace imap_rcube library with curl call

This commit removes the imap_rcube library with a curl call to the imap endpoint.
Since curl is a dependency of nextcloud this should not cause any issues.

This closes #116

Signed-off-by: Tim Wichmann <tim@wichmann.online>

lib/imap.php

@@ -8,8 +8,6 @@
  * See the COPYING-README file.
  */
 
-use OCA\user_external\imap\imap_rcube;
-
 /**
  * User authentication against an IMAP mail server
  *
@@ -87,31 +85,30 @@ public function checkPassword($uid, $password) {
 					$groups[] = $pieces[1];
 		}
 
-		$rcube = new imap_rcube();
-
-		$params = ["port"=>$this->port, "timeout"=>10];
+		$protocol = $this->sslmode ? "imaps" : "imap";
+		$url = "{$protocol}://{$this->mailbox}:{$this->port}";
+		$ch = curl_init();
+		curl_setopt($ch, CURLOPT_URL, $url);
+		curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
+		curl_setopt($ch, CURLOPT_USERPWD, $username.":".$password);
+		curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, 10);
 
-		$params["ssl_mode"] = $this->sslmode ? $this->sslmode : null;
-		$params["force_caps"] = false;
-		$canconnect = $rcube->connect(
-					$this->mailbox,
-					$username,
-					$password,
-					$params
-		);
+		$canconnect = curl_exec($ch);
 
 		if($canconnect) {
- 			$rcube->closeConnection();
+			curl_close($ch);
 			$uid = mb_strtolower($uid);
 			$this->storeUser($uid, $groups);
 			return $uid;
 		} else {
 			OC::$server->getLogger()->error(
-				'ERROR: Could not connect via roundcube lib: '.$rcube->error,
+				'ERROR: Could not connect to imap server via curl: '.curl_error($ch),
 				['app' => 'user_external']
 			);
 		}
 
+		curl_close($ch);
+
 		return false;
 	}
 }