问如何水平对齐bootstrap 4导航菜单？

EN

<nav class="navbar navbar-expand-md navbar-dark bg-dark fixed-top">
      <a class="navbar-brand" href="/">Payload Examples</a>
      <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarsExampleDefault" aria-controls="navbarsExampleDefault" aria-expanded="false" aria-label="Toggle navigation">
        <span class="navbar-toggler-icon"></span>
      </button>

      <div class="collapse navbar-collapse" id="navbarsExampleDefault">
        <ul class="navbar-nav mr-auto">
          <li class="nav-item active">
            <a class="nav-link" href="/">Home <span class="sr-only">(current)</span></a>
          </li>

          {% if session['name'] %}
          <li class="nav-item active">
              <a class="nav-link" style="cursor: default;" href="#" >Oauth Type: {{ session['auth_type'] }} </a>
            </li>
            <li>
              <a class="nav-link" href="{{ url_for('logout') }}" id="logout"
                 data-busy="href">Logout <span class="sr-only">(current)</span></a>
            </li>
          {% else %}
            <li>
              <label for='submit-form' class="nav-link" >Login</label> <span class="sr-only">(current)</span>
            </li>
          </ul>
          <div class="navbar-collapse collapse w-100 order-3 dual-collapse2">
            <ul class="navbar-nav ml-auto">
                  <li class="nav-item active"> <a class="navbar-brand" style="cursor: default;" href="#">Choose OAuth Scheme:</a></li>
                  <form action="{{ url_for('login') }}" method="POST"><select class="form-control" id="authType" name="authType">
                  <option>Auth</option>
                  <option>Grant</option>
                  <option disabled>Code</option>
                  </select>
                  <input type="submit" id="submit-form" class="hidden" />
                </form>
              <li>
                  <a class="nav-link mr-auto" target=_BLANK href="https://example.com/help">❔</a>
              </li>
            </ul>
          </ul>
          </div>
          {% endif %}
        </ul>
        {% if session['name'] %}
          <span class="navbar-text">
            Welcome {{ session['name'] }}
          </span>
        {% endif %}
      </div>
    </nav>