Adminer plugin for filling and/or auto-submitting the login form.

AdminerAutoLoginForm.php

<?php
/**
 * Adminer plugin for filling and/or auto-submitting the login form.
 *
 * This class allows you to pre-fill the Adminer login form fields
 * with predefined credentials, and optionally auto-submit
 * the form to perform an automatic login.
 *
 * Typical usage: instantiate the class with login parameters and call loginForm().
 *
 * @author Paul BOREL <paul.borel@gmail.com>
 */
class AdminerAutoLoginForm {
  /**
   * @var array Associative array with login parameters: system, server, name, pass, database.
   */
  private $params;

  /**
   * @var bool Indicates whether the form should be automatically submitted after filling.
   */
  private $autoSubmit;

  /**
   * Initializes the plugin to fill (and optionally auto-submit) the Adminer login form.
   *
   * The $params keys can be:
   *  - system : (string) database driver type. Possible values:
   *      - "server"  (MySQL)
   *      - "sqlite"  (SQLite3)
   *      - "sqlite2" (SQLite2)
   *      - "pgsql"   (PostgreSQL)
   *      - "oracle"  (Oracle)
   *      - "mssql"   (MS SQL)
   *      - "firebird" (Firebird alpha)
   *      - "simpledb" (SimpleDB)
   *      - "mongo"    (MongoDB)
   *      - "elastic"  (Elasticsearch)
   *  - server : (string) SQL server address/name, default ""
   *  - name : (string) SQL username, default ""
   *  - pass : (string) password, default ""
   *  - database : (string) database name, default ""
   *
   * @param array $params    Associative array of login parameters.
   * @param bool  $autoSubmit Whether to automatically submit the form after filling it (default true).
   */
  public function __construct(array $params = [], $autoSubmit = null) {
    $defaults = [
      'system' => $_ENV['ADMINER_DEFAULT_SYSTEM'] ?? 'server',
      'server' => $_ENV['ADMINER_DEFAULT_SERVER'] ?? '',
      'name' => $_ENV['ADMINER_DEFAULT_NAME'] ?? '',
      'pass' => $_ENV['ADMINER_DEFAULT_PASS'] ?? '',
      'database' => $_ENV['ADMINER_DEFAULT_DATABASE'] ?? '',
    ];
    $autoSubmit = $autoSubmit ?? (($_ENV['ADMINER_AUTOLOGIN_AUTOSUBMIT'] ?? 'false') === 'true');
    $this->params = array_merge($defaults, $params);
    $this->autoSubmit = $autoSubmit;
  }

  function name() {
    return null;
  }

  /**
   * Outputs JavaScript code to pre-fill and/or auto-submit the Adminer login form.
   *
   * The script is output only if the URL parameters do not already contain
   * the login information (driver, username, db).
   *
   * @return null
   */
  public function loginForm() {
    $empty = empty($_GET[Adminer\DRIVER] ?? '') &&
      empty($_GET['username'] ?? '') &&
      empty($_GET['db'] ?? '');
    if (
      $empty || (
      ($_GET[Adminer\DRIVER] ?? '' === $this->params['server'])
      )
    ) {
      $fields = [
        'auth[server]' => $this->params['server'],
        'auth[username]' => $this->params['name'],
        'auth[password]' => $this->params['pass'],
        'auth[db]' => $this->params['database']
      ];
      ?>
      <script<?= Adminer\nonce(); ?>>
        document.addEventListener("DOMContentLoaded", function() {
          // Select the driver in the dropdown
          var dr = document.querySelector('option[value="<?= htmlspecialchars($this->params['system']) ?>"]');
          if(dr) dr.selected = true;

          // Auto-fill the form fields
          <?php foreach($fields as $name => $value): if($value): ?>
          var el = document.querySelector('input[name="<?= htmlspecialchars($name) ?>"]');
          if(el && el.value.trim() === "") el.value = "<?= addslashes($value) ?>";
          <?php endif; endforeach; ?>

          // Automatically submit the form if enabled
          <?php if($empty && $this->autoSubmit): ?>
          var btn = document.querySelector('input[type="submit"]');
          if(btn) btn.click();
          <?php endif; ?>
        });
      </script>
      <?php
    }
    return null;
  }
}

I couldn't get it working with the ADMINER_PLUGINS environment variable and the mount, but I now notice a difference between /plugins and /plugins-enabled: that might have been the reason it didn't work for me. I probably mixed them up.

Just for completeness' sake: I now have the plugin file (with return new AdminerAutoLoginForm(); at the end) in some directory that I mount as /plugins-enabled, without specifying ADMINER_PLUGINS:

volumes:
  - ../dir-with-the-php-file/:/var/www/html/plugins-enabled