If you want your users to be able to connect with both Joomla login and SSO, you can add the button in the template :
To do this, you will have to go to
/administrator > Extensions > Templates > templates > Rt_Galatea
Choose the following file : html/ mod_login/default.php
and replace
<div id="form-login-submit" class="control-group">
<div class="controls">
<button type="submit" tabindex="0" name="Submit" class="btn btn-primary login-button"><?php echo JText::_('JLOGIN'); ?></button>
</div>
</div>
par
<div id="form-login-submit" class="control-group">
<div class="controls">
<button type="submit" tabindex="0" name="Submit" class="btn btn-primary login-button"><?php echo JText::_('JLOGIN'); ?></button>
<a href="?morequest=sso" class="btn btn-primary login-button">SSO</a>
</div>
</div>
Same thing for html/com_users/default_login.php
You just have to add the
<a href="?morequest=sso" class="btn btn-primary login-button">SSO</a>
If you only have default-#datetime#.php make a copy of one of them and rename it default.php