openproject/app/views/hooks/login/_auth_provider.html.erb

<%#-- copyright
OpenProject is a project management system.
Copyright (C) 2012-2018 the OpenProject Foundation (OPF)

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License version 3.

OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
Copyright (C) 2006-2017 Jean-Philippe Lang
Copyright (C) 2010-2013 the ChiliProject Team

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

See docs/COPYRIGHT.rdoc for more details.

++#%>

<% unless Rails.env.production? %>
  <%
    opts = {}

    if params['back_url']
      opts[:origin] = params['back_url']
    end
  %>
  <a href="<%= omniauth_start_path(:developer, opts) %>" class="auth-provider auth-provider-developer button">
    <span class="auth-provider-name">Omniauth Developer</span>
  </a>
<% end %>