ldap/src/main/java/org/springframework/security/ldap/authentication/SpringSecurityAuthenticationSource.java
public String getPrincipal() {
		Authentication authentication = SecurityContextHolder.getContext()
				.getAuthentication();

		if (authentication == null) {
			log.warn("No Authentication object set in SecurityContext - returning empty String as Principal");
			return "";
		}

		Object principal = authentication.getPrincipal();

		if (principal instanceof LdapUserDetails) {
			LdapUserDetails details = (LdapUserDetails) principal;
			return details.getDn();
		}
		else if (authentication instanceof AnonymousAuthenticationToken) {
			if (log.isDebugEnabled()) {
				log.debug("Anonymous Authentication, returning empty String as Principal");
			}
			return "";
		}
		else {
			throw new IllegalArgumentException(
					"The principal property of the authentication object"
							+ "needs to be an LdapUserDetails.");
		}
	}
public String getPrincipal() {
		Authentication authentication = SecurityContextHolder.getContext()
				.getAuthentication();

		if (authentication == null) {
			log.warn("No Authentication object set in SecurityContext - returning empty String as Principal");
			return "";
		}

		Object principal = authentication.getPrincipal();

		if (principal instanceof LdapUserDetails) {
			LdapUserDetails details = (LdapUserDetails) principal;
			return details.getDn();
		}
		else if (authentication instanceof AnonymousAuthenticationToken) {
			if (log.isDebugEnabled()) {
				log.debug("Anonymous Authentication, returning empty String as Principal");
			}
			return "";
		}
		else {
			throw new IllegalArgumentException(
					"The principal property of the authentication object"
							+ "needs to be an LdapUserDetails.");
		}
	}
Get the principals of the logged in user, in this case the distinguished name.

@return the distinguished name of the logged in user.