[[servlet-webclient]]
= WebClient for Servlet Environments

[NOTE]
====
The following documentation is for use within Servlet environments.
For all other environments, refer to <<webclient, WebClient for Reactive>> environments.
====


Spring Framework has built in support for setting a Bearer token.

[source,java]
----
webClient.get()
    .headers(h -> h.setBearerAuth(token))
    ...
----

Spring Security builds on this support to provide additional benefits:

* Spring Security will automatically refresh expired tokens (if a refresh token is present)
* If an access token is requested and not present, Spring Security will automatically request the access token.
** For authorization_code this involves performing the redirect and then replaying the original request
** For client_credentials the token is simply requested and saved
* Support for the ability to transparently include the current OAuth token or explicitly select which token should be used.

[[servlet-webclient-setup]]
== WebClient OAuth2 Setup

The first step is ensuring to setup the `WebClient` correctly.
An example of setting up `WebClient` in a servlet environment can be found below:

[source,java]
----
@Bean
WebClient webClient(ClientRegistrationRepository clientRegistrations,
		OAuth2AuthorizedClientRepository authorizedClients) {
	ServletOAuth2AuthorizedClientExchangeFilterFunction oauth =
			new ServletOAuth2AuthorizedClientExchangeFilterFunction(clientRegistrations, authorizedClients);
	// (optional) explicitly opt into using the oauth2Login to provide an access token implicitly
	// oauth.setDefaultOAuth2AuthorizedClient(true);
	// (optional) set a default ClientRegistration.registrationId
	// oauth.setDefaultClientRegistrationId("client-registration-id");
	return WebClient.builder()
			.apply(oauth2.oauth2Configuration())
			.build();
}
----

[[servlet-webclient-implicit]]
== Implicit OAuth2AuthorizedClient

If we set `defaultOAuth2AuthorizedClient` to `true` in our setup and the user authenticated with oauth2Login (i.e. OIDC), then the current authentication is used to automatically provide the access token.
Alternatively,  if we set `defaultClientRegistrationId` to a valid `ClientRegistration` id, that registration is used to provide the access token.
This is convenient, but in environments where not all endpoints should get the access token, it is dangerous (you might provide the wrong access token to an endpoint).

[source,java]
----
Mono<String> body = this.webClient
		.get()
		.uri(this.uri)
		.retrieve()
		.bodyToMono(String.class);
----

[[servlet-webclient-explicit]]
== Explicit OAuth2AuthorizedClient

The `OAuth2AuthorizedClient` can be explicitly provided by setting it on the request attributes.
In the example below we resolve the `OAuth2AuthorizedClient` using Spring WebFlux or Spring MVC argument resolver support.
However, it does not matter how the `OAuth2AuthorizedClient` is resolved.

[source,java]
----
@GetMapping("/explicit")
Mono<String> explicit(@RegisteredOAuth2AuthorizedClient("client-id") OAuth2AuthorizedClient authorizedClient) {
	return this.webClient
			.get()
			.uri(this.uri)
			.attributes(oauth2AuthorizedClient(authorizedClient))
			.retrieve()
			.bodyToMono(String.class);
}
----


[[servlet-webclient-clientregistrationid]]
== clientRegistrationId

Alternatively, it is possible to specify the `clientRegistrationId` on the request attributes and the `WebClient` will attempt to lookup the `OAuth2AuthorizedClient`.
If it is not found, one will automatically be acquired.

[source,java]
----
Mono<String> body = this.webClient
		.get()
		.uri(this.uri)
		.attributes(clientRegistrationId("client-id"))
		.retrieve()
		.bodyToMono(String.class);
----
