cas/src/main/java/org/springframework/security/cas/authentication/CasAuthenticationProvider.java
protected UserDetails loadUserByAssertion(final Assertion assertion) {
		final CasAssertionAuthenticationToken token = new CasAssertionAuthenticationToken(
				assertion, "");
		return this.authenticationUserDetailsService.loadUserDetails(token);
	}
protected UserDetails loadUserByAssertion(final Assertion assertion) {
		final CasAssertionAuthenticationToken token = new CasAssertionAuthenticationToken(
				assertion, "");
		return this.authenticationUserDetailsService.loadUserDetails(token);
	}
Template method for retrieving the UserDetails based on the assertion. Default is
to call configured userDetailsService and pass the username. Deployers can override
this method and retrieve the user based on any criteria they desire.

@param assertion The CAS Assertion.
@return the UserDetails.