URL found in auth.gsp - beginner - grails

Question

I need to know the following. I copied the following code from auth.gsp. I need to know what:
1.) I need to know what '${postUrl}' means?
2.) I did copy this code and paste it in another GSP called index.gsp, but the page didn't login successfully.
<form action='${postUrl}' method='POST' id="loginForm" name="loginForm" autocomplete='off'>
<div class="sign-in">
<h1><g:message code='spring.security.ui.login.signin'/></h1>
<table>
<tr>
<td><label for="username"><g:message code='spring.security.ui.login.username'/></label></td>
<td><input name="j_username" id="username" size="20" /></td>
</tr>
<tr>
<td><label for="password"><g:message code='spring.security.ui.login.password'/></label></td>
<td><input type="password" name="j_password" id="password" size="20" /></td>
</tr>
<tr>
<td colspan='2'>
<input type="checkbox" class="checkbox" name="${rememberMeParameter}" id="remember_me" checked="checked" />
<label for='remember_me'><g:message code='spring.security.ui.login.rememberme'/></label> |
<span class="forgot-link">
<g:link controller='register' action='forgotPassword'><g:message code='spring.security.ui.login.forgotPassword'/></g:link>
</span>
</td>
</tr>
<tr>
<td colspan='2'>
<s2ui:linkButton elementId='register' controller='register' messageCode='spring.security.ui.login.register'/>
<s2ui:submitButton elementId='loginButton' form='loginForm' messageCode='spring.security.ui.login.login'/>
</td>
</tr>
</table>
</div>
</form>

Answer 1

Spring security work on filters. If you print postUrl in your gsp file then it looks like /myApp/j_spring_security_check, only /j_spring_security_check URL is processed by Spring Security filter.
If you past auth.gap and not sending this url then cannot login. Change your gsp slightly to make this run, replace ${postUrl} with ${createLink(uri: '/j_spring_security_check')}.