openid/src/main/java/org/springframework/security/openid/OpenIDAuthenticationFilter.java
protected String obtainUsername(HttpServletRequest req) {
		String claimedIdentity = req.getParameter(claimedIdentityFieldName);

		if (!StringUtils.hasText(claimedIdentity)) {
			logger.error("No claimed identity supplied in authentication request");
			return "";
		}

		return claimedIdentity.trim();
	}
protected String obtainUsername(HttpServletRequest req) {
		String claimedIdentity = req.getParameter(claimedIdentityFieldName);

		if (!StringUtils.hasText(claimedIdentity)) {
			logger.error("No claimed identity supplied in authentication request");
			return "";
		}

		return claimedIdentity.trim();
	}
Reads the <tt>claimedIdentityFieldName</tt> from the submitted request.