Forwarded headers are now processed before ServerWebExchange is created
through ForwardedHeaderTransformer which has the same logic as the
ForwardedHeaderFilter but works on the request only.

ForwardedHeaderFilter is deprecated as of 5.1 but if registered it is
removed from the list of filters and ForwardedHeaderTransformer is used
instead.

Issue: SPR-17072

Issue: SPR-17109

This commit introduces Protobuf support in WebFlux via dedicated
codecs.

Flux<Message> are serialized/deserialized using delimited Protobuf
messages with the size of each message specified before the message
itself. In that case, a "delimited=true" parameter is added to the
content type.

Mono<Message> are expected to use regular Protobuf message
format (without the size prepended before the message).

Related HttpMessageReader/Writer are automatically registered when the
"com.google.protobuf:protobuf-java" library is detected in the classpath,
and can be customized easily if needed via CodecConfigurer, for example
to specify protocol extensions via the ExtensionRegistry based
constructors.

Both "application/x-protobuf" and "application/octet-stream" mime types
are supported.

Issue: SPR-15776

Preparation for SPR-17072

Preparation for SPR-17072

In order to be consistent with SPR-15776, and since it does not
provide clear added value, this commit deprecates
ExtensionRegistryInitializer and uses ExtensionRegistry
parameter instead in ProtobufHttpMessageConverter and
ProtobufJsonFormatHttpMessageConverter constructors.

Issue: SPR-17081

Issue: SPR-16418

Since SPR-15205, the `FormHttpMessageConverter` is adding a `charset`
directive to the `Content-Type` request header in order to help servers
understand which charset is being used to encode headers of each part.

As reported in SPR-17030 and others, some servers are not parsing
properly such header values and assume that `boundary` is the last
directive in the `Content-Type` header.

This commit reorders the charset information right before the boundary
declaration to get around those issues.

Issue: SPR-17030

Issue: SPR-16946

See Javadoc on UriComponentsBuilder#uriVariables for details.

This helps to prepare for SPR-17027 where the MvcUriComponentsBuilder
already does a partial expand but was forced to build UriComonents
and then create a new UriComponentsBuilder from it to continue. This
change makes it possible to stay with the same builder instance.

Issue: SPR-17027

After the latest changes, two small fixes in the clone method to copy
the encode flag, and in the encodeUriTemplate method to account for
possible null query params.

Improvements in the URI encoding section.

Issue: SPR-17039, SPR-17027

+ minor update to the InMemoryWebSession to match the defined behavior.

Issue: SPR-17051

DefaultUriBuilderFactory now uses EncodingMode.TEMPLATE_AND_VALUES by
default. However the RestTemplate explicitly sets it to the previous
setting EncodingMode.URI_COMPONENTS, so this affects mainly the
WebClient and any direct use of DefaultUriBuilderFactory to configure
either the RestTemplate or the WebClient.

Issue: SPR-17039

Issue: SPR-17039

The ability to request to encode before `build()`, and more importantly
before expanding, allows stricter encoding to be applied to URI vars
and consequently to neutralize the effect of characters with reserved
meaning in a URI.

Issue: SPR-17039

This commit removes the session threshold check added recently which
is not effective since maxIdleTime is usually much longer than the
frequency of checks. The lazy triggering of expiration checks during
create or retreive are simple and the most effective

This commit also adds a maxSessions limit on the total number of
sessions that can be created at any one time, a getSessions method
for management purposes, and a removeExpiredSessions public API
for manual triggering of expiration checks.

Issue: SPR-17020, SPR-16713

1. Add session count threshold as am extra pre-condition.
2. Check pre-conditions for expiration checks on every request.

Effectively an upper bound on how many sessions can be created before
expiration checks are performed.

Issue: SPR-17020

Issue: SPR-16203

Issue: SPR-16997

This commit changes the Basic Authentication Consumer<HttpHeaders> to
a basic setBasicAuth(String, String) method.

Issue: SPR-16913

Issue: SPR-16966

Issue: SPR-15588

Includes specific fine-tuning of ProtobufHttpMessageConverter and JAXB2 based message converters, as well as revised javadoc for abstract base classes.

Issue: SPR-16995

Issue: SPR-16913

Issue: SPR-16988

Issue: SPR-16980

Update tests to ensure that tabs are used instead of spaces. Also
consistently apply a new line at the end of each file.

Issue: SPR-16968

Polish a few issue identified when adding checkstyle to the
build. Although checkstyle is not enforcing rules on tests,
these are a few minor changes that are still worth making.

Issue: SPR-16968

Issue: SPR-16972

Issue: SPR-16898