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 = true) {
    $defaults = [
      "system"   => "server",
      "server"   => "",
      "name"     => "",
      "pass"     => "",
      "database" => "",
    ];
    $this->params = array_merge($defaults, $params);
    $this->autoSubmit = $autoSubmit;
  }


  /**
    * 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() {
    if (
      empty($_GET[Adminer\DRIVER] ?? "") && 
      empty($_GET["username"] ?? "") && 
      empty($_GET["db"] ?? "")
    ) {
      $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($this->autoSubmit): ?>
        var btn = document.querySelector('input[type="submit"]');
        if(btn) btn.click();
        <?php endif; ?>
      });
      </script>
      <?php
    }
    return null;
  }
}

Here's a version which works with the adminer docker image - https://gist.github.com/codebymikey/518d60237143424ca6073dcec23d6bd2 entirely via environment variables and ADMINER_PLUGINS without needing to mount /var/www/html/plugins/autologin-form.php and /var/www/html/plugins-enabled/autologin-form.php.

Feel free to apply the changes there on the main version.