* {@code LoginModule} or {@code null}.
*/
@CheckForNull
protected SecurityProvider getSecurityProvider() {
if (securityProvider == null && callbackHandler != null) {
SecurityProviderCallback scb = new SecurityProviderCallback();
try {
callbackHandler.handle(new Callback[] {scb});
securityProvider = scb.getSecurityProvider();
} catch (UnsupportedCallbackException e) {
log.debug(e.getMessage());
} catch (IOException e) {
log.debug(e.getMessage());
}