Configuring Geoserver to use a proxy when accessing external services?

I don't want to access my geoserver behind a proxy. I can access it directly. It is in same network as I with no proxy between us.

I have a Geoserver and created some layers consuming WMS services from somewhere.

My problem is that my geoserver is behind a proxy. its a governamental institution and all access to external world needs to authenticate do the proxy to go out. I need to configure it in my browser to use the internet, but need an exclusion rule in browser to access internal network (to ignore proxy).

I don't know how to tell Geoserver to login into that proxy to allow it access the outside WMS service I need to consume.

The result is as follow:

2016-05-02 10:03:59,749 ERROR [org.geoserver.ows] - 
org.geoserver.platform.ServiceException: Internal error 

    at org.geoserver.wms.GetMap.run(GetMap.java:129)
    at org.geoserver.wms.DefaultWebMapService.getMap(DefaultWebMapService.java:320)
    at sun.reflect.GeneratedMethodAccessor300.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:319)
...
Caused by: java.io.IOException: Server returned HTTP error code 407 for URL http://mapas.icmbio.gov.br/i3geo/ogc.php?TEMA=uc_esec&REQUEST=GetCapabilities&VERSION=1.3.0&SERVICE=WMS
    at org.geotools.data.ows.MultithreadedHttpClient.get(MultithreadedHttpClient.java:202)
    at org.geotools.data.ows.AbstractOpenWebService.internalIssueRequest(AbstractOpenWebService.java:426)

    at org.geotools.data.wms.WebMapServer.issueRequest(WebMapServer.java:419)
    at org.geotools.data.ows.AbstractOpenWebService.negotiateVersion(AbstractOpenWebService.java:260)
    at org.geotools.data.ows.AbstractOpenWebService.(AbstractOpenWebService.java:110)
    at org.geotools.data.wms.WebMapServer.(WebMapServer.java:382)
    at org.geoserver.catalog.ResourcePool.getWebMapServer(ResourcePool.java:1653)
    at org.geoserver.catalog.impl.WMSStoreInfoImpl.getWebMapServer(WMSStoreInfoImpl.java:102)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)

    at org.geoserver.catalog.impl.ModificationProxy.invoke(ModificationProxy.java:146)
    at com.sun.proxy.$Proxy6.getWebMapServer(Unknown Source)
    at org.geoserver.wms.GetMap.executeInternal(GetMap.java:464)
    at org.geoserver.wms.GetMap.run(GetMap.java:248)
    at org.geoserver.wms.GetMap.run(GetMap.java:119)

To go to http://mapas.icmbio.gov.br/i3geo/ogc.php?TEMA=uc_esec&REQUEST=GetCapabilities&VERSION=1.3.0&SERVICE=WMS it needs to login into same proxy I have configured in my browser (to go outside my network)

My proxy allow url auth like :@:

2016-05-02 10:03:53,627 DEBUG [org.geotools.data.ows] - Found 'http.proxyHost' Java System property. Using it as proxy server. Port: 6060
2016-05-02 10:03:53,627 DEBUG [org.geotools.data.ows] - Initialized with nonProxyHosts: [localhost, 10.5.115.122, 10.5.115.123, *.defesa.mil.br, 10.5.115.136, 10.5.115.110, 10.5.115.22, siglmd-app.defesa.mil.br]

2016-05-02 10:03:53,628 DEBUG [org.geotools.data.ows] - System property http.proxyUser and http.proxyPassword found, setting proxy auth credentials
2016-05-02 10:03:59,749 ERROR [org.geotools.data.ows] - Failed to execute request http://mapas.icmbio.gov.br/i3geo/ogc.php?TEMA=uc_esec&REQUEST=GetCapabilities&VERSION=1.3.0&SERVICE=WMS
2016-05-02 10:03:59,749 ERROR [org.geoserver.ows] - 
org.geoserver.platform.ServiceException: Internal error 
    at org.geoserver.wms.GetMap.run(GetMap.java:129)
    at org.geoserver.wms.DefaultWebMapService.getMap(DefaultWebMapService.java:320)
    at sun.reflect.GeneratedMethodAccessor300.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:319)

EDIT: Strange... some links are working others don't. This service gives me a Server returned HTTP response code: 407 for URL: http://mapas.icmbio.gov.br/i3geo/ogc.php?tema=uc_esec&service=wms&request=getcapabilities and this don't: http://sigel.aneel.gov.br/arcgis/services/SIGEL/Distribuicao/MapServer/WMSServer. I conclude it is not problem in my proxy since I can go outside in some cases...

Other cases: Work:

http://sigel.aneel.gov.br/arcgis/services/SIGEL/Transmissao/MapServer/WMSServer?service=WMS&version=1.1.0&request=GetCapabilities

Don't work ( error 407 ):

http://geoportal.lneg.pt/arcgis/services/RecursosHidro/MapServer/WMSServer?request=GetCapabilities&service=WMS&version=1.1.0

Geoserver proxy auth implementaion problem? https://stackoverflow.com/questions/14113341/http-407-proxy-authentication-required-how-to-handle-in-java-code

EDIT

This must be corrected to accept a password and an user name:

Still receiving Internal error : Server returned HTTP error code 407 for URL http://XYZ/?REQUEST=GetCapabilities&VERSION=1.3.0&SERVICE=WMS because it is ignoring username and password from -Dxxx configuration.