diff --git a/plugins/login-external.php b/plugins/login-external.php
new file mode 100644
index 00000000..20926bb5
--- /dev/null
+++ b/plugins/login-external.php
@@ -0,0 +1,138 @@
+<?php
+
+/**
+ * Enables use of saved credentials for accessing a database, without divulging
+ * them. Provides a mechanism to authenticate each request against any login
+ * system external to Adminer, or to bypass authentication (for local
+ * development on a private machine).
+ *
+ * @author Roy Orbitson, https://github.com/Roy-Orbison
+ * @license https://www.apache.org/licenses/LICENSE-2.0 Apache License, Version 2.0
+ * @license https://www.gnu.org/licenses/gpl-2.0.html GNU General Public License, version 2 (one or other)
+ */
+
+class AdminerLoginExternal {
+
+	protected $externals;
+
+	/**
+	 * Provide access details of your database, the current user's authentication status, and other config.
+	 *
+	 * @param array|object $externals An enumeration containing the fields normally completed on the login form:
+	 *                                server
+	 *                                database (optional, but recommended. user can always access any db the credentials allow)
+	 *                                username
+	 *                                password
+	 *                                driver (defaults to 'server' for MySQL, but must be specified otherwise,
+	 *                                        e.g. 'pgsql', 'sqlite')
+	 *
+	 *                                Plus fields to control the behaviour of this plugin:
+	 *                                authenticated (required boolean, ideally checked on *every* request, true if the
+	 *                                               user is known, currently authenticated, and has db privileges
+	 *                                               equivalent to the specified username)
+	 *                                app_name (dynamically change the name of the tool from Adminer/AdminerEvo)
+	 *                                manual_login (optional boolean to control auto-submission of Adminer's own login
+	 *                                              form, and prevents logging out whilst authenticated)
+	 *                                expired_html (optional HTML message to show when user's external authentication
+	 *                                              expires whilst logged in to Adminer)
+	 *                                failure_html (optional HTML message to show user they are not authenticated, e.g. a
+	 *                                              paragraph containing a link to the login page)
+	 */
+	function __construct($externals) {
+		$externals = (object) $externals;
+		if (empty($externals->driver)) {
+			$externals->driver = 'server';
+		}
+		if (isset($_POST['auth'])) {
+			$_POST['auth']['driver'] = $externals->driver;
+			$_POST['auth']['server'] = $_POST['auth']['username'] = $_POST['auth']['password'] = '';
+		}
+		$this->externals = $externals;
+	}
+
+	function name() {
+		return empty($this->externals->app_name) ? null : $this->externals->app_name;
+	}
+
+	function credentials() {
+		if (empty($this->externals->authenticated)) {
+			# always check external stat rather than relying on adminer's session login
+			auth_error(
+				empty($this->externals->expired_html) ?
+					'External authentication expired.' :
+					$this->externals->expired_html
+			);
+			return false;
+		}
+		return [
+			$this->externals->server,
+			$this->externals->username,
+			$this->externals->password,
+		];
+	}
+
+	function database() {
+		return empty($this->externals->database) ? null : $this->externals->database;
+	}
+
+	function loginForm() {
+		if (empty($this->externals->authenticated)) {
+			if (empty($this->externals->failure_html)) {
+				echo '<p>You must first log in to the system that grants access to this tool.</p>';
+			}
+			else {
+				echo $this->externals->failure_html;
+			}
+			return false;
+		}
+
+		if (empty($this->externals->manual_login)) {
+			echo script(
+				<<<EOJS
+document.addEventListener(
+	'DOMContentLoaded',
+	function() {
+		document.forms[0].submit();
+	},
+	true
+);
+EOJS
+			);
+		}
+	}
+
+	function loginFormField($name, $heading) {
+		# only for user's benefit, submitted values are overridden by config
+		$value = '';
+		switch ($name) {
+			case 'db':
+				$value = h(isset($_GET['username']) ? (isset($_GET['db']) ? $_GET['db'] : '') : $this->database());
+				return <<<EOHTML
+$heading<input type="text" name="auth[$name]" value="$value">
+
+EOHTML;
+			case 'driver':
+				if (function_exists('get_driver')) {
+					$value = h($this->externals->driver);
+					$driver = h(get_driver($this->externals->driver)) ?: 'Unknown';
+					return <<<EOHTML
+$heading<input type="hidden" name="auth[$name]" value="$value">$driver
+
+EOHTML;
+				}
+				$value = ' value="' . h($this->externals->driver) . '"';
+				# don't break
+			case 'server':
+			case 'username':
+			case 'password':
+				return <<<EOHTML
+<input type="hidden" name="auth[$name]"$value>
+
+EOHTML;
+		}
+	}
+
+	function login($login, $password) {
+		return !empty($this->externals->authenticated);
+	}
+}