code: @RequestMapping(value="/{providerId}", method=RequestMethod.POST)
  	public RedirectView connect(@PathVariable String providerId, NativeWebRequest request) {
  		ConnectionFactory<?> connectionFactory = connectionFactoryLocator.getConnectionFactory(providerId);
  		MultiValueMap<String, String> parameters = new LinkedMultiValueMap<String, String>(); 
  		preConnect(connectionFactory, parameters, request);
  		try {
  			return new RedirectView(connectSupport.buildOAuthUrl(connectionFactory, request, parameters));
  		} catch (Exception e) {
  			sessionStrategy.setAttribute(request, PROVIDER_ERROR_ATTRIBUTE, e);
  			return connectionStatusRedirect(providerId, request);
  		}
  	}
docs: Process a connect form submission by commencing the process of establishing a connection to the provider on behalf of the member.
  For OAuth1, fetches a new request token from the provider, temporarily stores it in the session, then redirects the member to the provider's site for authorization.
  For OAuth2, redirects the user to the provider's site for authorization.
  @param providerId the provider ID to connect to
  @param request the request
  @return a RedirectView to the provider's authorization page or to the connection status page if there is an error