Properly handle proxified requests in backend services delegating to Spring-boot ForwardedHeaderFilter

[groldan]

Properly handle proxified requests in backend services delegating to Spring-boot ForwardedHeaderFilter

GeoServer uses a URLMangler extension point to make changes to exposed
URL's.

To deal with proxyfied requests, it relies in a ProxifyingUrlMangler
implementation, which can look at X-Forwarded-* HTTP request headers
and adapt URL's accordingly.

GeoServer-cloud had its own CloudProxifyingURLMangler extension point
implementation which relied on the same X-Forwarded-* request headers.

Problem is, one of the headers Geoserver relies on is X-Forwarded-Path,
which is an unofficial header, instead of the official X-Forwarded-Prefix.

By setting the config property server.forward-headers-strategy: framework
in all services bootstrap.yml files, we now let spring-boot's
ForwardedHeaderFilter take care of reflecting the client-originated
protocol and address in the HttpServletRequest, and hence don't need
the URLMangler to perform proxy-related adaptations anymore.

Also works when the gateway is behind another proxy, as long as it sends the Forwarded
(and X-Forwarded-Prefix if needed) headers.

For example, a direct request to the gateway would return:

curl -s  "http://localhost:9090/wfs?request=getcapabilities&version=1.1.0" | xmllint --format -|grep http|head -n 5
<wfs:WFS_Capabilities xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.opengis.net/wfs" xmlns:wfs="http://www.opengis.net/wfs" xmlns:ows="http://www.opengis.net/ows" xmlns:gml="http://www.opengis.net/gml" xmlns:ogc="http://www.opengis.net/ogc" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:osm="http://geoserver.org/osm" xmlns:test="http://test2.com" version="1.1.0" xsi:schemaLocation="http://www.opengis.net/wfs http://localhost:9090/schemas/wfs/1.1.0/wfs.xsd" updateSequence="343">
          <ows:Get xlink:href="http://localhost:9090/wfs"/>
          <ows:Post xlink:href="http://localhost:9090/wfs"/>
          <ows:Get xlink:href="http://localhost:9090/wfs"/>
          <ows:Post xlink:href="http://localhost:9090/wfs"/>

While a proxied request would result in:

curl -s \
 -H "Forwarded: proto=https;host=edge.test.com:1111;for=10.0.0.1:8080" \
 -H "X-Forwarded-Prefix: /geoserver/cloud" \
 "http://localhost:9090/wfs?request=getcapabilities&version=1.1.0" | xmllint --format -|grep http|head -n 5

<wfs:WFS_Capabilities xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.opengis.net/wfs" xmlns:wfs="http://www.opengis.net/wfs" xmlns:ows="http://www.opengis.net/ows" xmlns:gml="http://www.opengis.net/gml" xmlns:ogc="http://www.opengis.net/ogc" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:osm="http://geoserver.org/osm" xmlns:test="http://test2.com" version="1.1.0" xsi:schemaLocation="http://www.opengis.net/wfs https://edge.test.com:1111/geoserver/cloud/schemas/wfs/1.1.0/wfs.xsd" updateSequence="343">
          <ows:Get xlink:href="https://edge.test.com:1111/geoserver/cloud/wfs"/>
          <ows:Post xlink:href="https://edge.test.com:1111/geoserver/cloud/wfs"/>
          <ows:Get xlink:href="https://edge.test.com:1111/geoserver/cloud/wfs"/>
          <ows:Post xlink:href="https://edge.test.com:1111/geoserver/cloud/wfs"/>