OAuth2AuthorizationRequest.Builder should configure additional parameters with a consumer

[jzheaux]

In order to add a custom parameter to the default authorization request, an application follows the delegator pattern:

OAuth2AuthorizationRequestResolver delegate =
		new DefaultOAuth2AuthorizationRequestResolver
				(this.clients, "/oauth2/authorization");
return new OAuth2AuthorizationRequestResolver() {
	@Override
	public OAuth2AuthorizationRequest resolve(HttpServletRequest request) {
		return resolve(request, request.getServerName());
	}

	@Override
	public OAuth2AuthorizationRequest resolve
			(HttpServletRequest request, String clientRegistrationId) {
		OAuth2AuthorizationRequest authorizationRequest = 
				delegate.resolve(request);
		if (authorizationRequest == null) {
			return authorizationRequest;
		}
		Map<String, Object> parameters = new HashMap<>		
				(authorizationRequest.getAdditionalParameters());
		parameters.put("kc_idp_hint", clientRegistrationId);
		return OAuth2AuthorizationRequest.from(authorizationRequest)
				.additionalParameters(parameters)
				.build();
	}
};

It's quite easy to forget that the additionalParameters method overrides any parameters already set by the default implementation:

// ...
Map<String, Object> parameters = new HashMap<>		
		(authorizationRequest.getAdditionalParameters()); // <-- easy to forget
parameters.put("kc_idp_hint", clientRegistrationId);
return OAuth2AuthorizationRequest.from(authorizationRequest)
		.additionalParameters(parameters)
		.build();

This can be simplified by introducing a new configuration method that is also in line with other builders in Spring Security:

public Builder additionalParameters(Consumer<Map<String, Object>> parametersConsumer)

Given that method, the configuration would change to:

return OAuth2AuthorizationRequest.from(authorizationRequest)
		.additionalParameters(params -> params
				.put("kc_idp_hint", clientRegistrationId))
		.build();

Which also has the benefit that there is less code for the application.

[jzheaux]

Closed in favor of #7748