Disable redirects by default in TestRestTemplate for all HTTP clients

[quaff]

My test is broken after rest-assured dependency removed, I found it caused by TestRestTemplate inconsistent follow redirects. TestRestTemplate will use apache httpclient since org.apache.httpcomponents: httpclient is introduced by rest-assured, following redirects is disabled by default, thanks to #1497, you can enable it by passing HttpClientOption.ENABLE_REDIRECTS.
If apache httpclient is not present, TestRestTemplate will fallback to okhttp3:

spring-boot/spring-boot-project/spring-boot/src/main/java/org/springframework/boot/web/client/ClientHttpRequestFactorySupplier.java

Lines 41 to 45 in 47516b5

	Map<String, String> candidates = new LinkedHashMap<>();
	candidates.put("org.apache.http.client.HttpClient",
	"org.springframework.http.client.HttpComponentsClientHttpRequestFactory");
	candidates.put("okhttp3.OkHttpClient", "org.springframework.http.client.OkHttp3ClientHttpRequestFactory");
	REQUEST_FACTORY_CANDIDATES = Collections.unmodifiableMap(candidates);

okhttp3 enable following redirects by default, I think TestRestTemplate should keep same behavior not matter which underlying implementation, disabling following redirects is sensible since test want to know which url is redirected to, and it would be better if this option can be mutated.

[quaff]

Implementation	Default
HttpComponentsClientHttpRequestFactory	false
OkHttp3ClientHttpRequestFactory	true
SimpleClientHttpRequestFactory	true

[wilkinsona]

Thanks for the suggestion. As described in the javadoc, the current behaviour is expected:

If Apache Http Client 4.3.2 or better is available (recommended) it will be used as the client, and by default configured to ignore cookies and redirects.

We can explore the possibility of doing the same for other clients.

[quaff]

Or provide a mutate method withFollowRedirects like withBasicAuth for TestRestTemplate.

[quaff]

@philwebb TestRestTemplate use FOLLOW_WHEN_POSSIBLE since 3.4.0, it breaks tests that rely on DONT_FOLLOW.

EDIT: it's caused by followRedirects of jdk.internal.net.http.HttpClientImpl changed from NEVER to NORMAL after upgrading to 3.4.0.