Documentation for Pre/Post Login/Registration Handlers

[saimaddali]

The handlers are already in the SDK but aren't included in the docs.

I think our express docs do a good job of explaining the function of these: https://docs.stormpath.com/nodejs/express/latest/registration.html#pre-registration-handler

[tullo]

The WebHandler JavaDoc currently only references https://github.com/stormpath/stormpath-framework-spec/blob/master/handlers.md

[tullo]

Found some more info about spring beans that can be overwritten to implement custom handler logic

AbstractStormpathWebMvcConfiguration.java, StormpathWebSecurityConfigurer.java :

@Autowired(required = false)
@Qualifier("loginPreHandler")
protected WebHandler loginPreHandler = new DisabledWebHandler();

@Autowired(required = false)
@Qualifier("loginPostHandler")
protected WebHandler loginPostHandler = new DisabledWebHandler();

@Autowired(required = false)
@Qualifier("registerPreHandler")
protected WebHandler registerPreHandler = new DisabledWebHandler();

@Autowired(required = false)
@Qualifier("registerPostHandler")
protected WebHandler registerPostHandler = new DisabledWebHandler();