Install fails if HTTP Basic Auth is used between client and reverse proxy

To reproduce this error

1. Setup Apache in order to proxy requests to the Confluence instance
2. Configure it in order to asks for HTTP Basic Authentication
3. Then, when you try to use the Confluence installer, you'll get this message :

   The SystemInformationService could not be retrieved from the container. Therefore very limited information is available in this error report. 
   The SystemInformationService could not be retrieved due to the following error: java.lang.IllegalStateException: Spring Application context has not been set
   

   With this Cause :

   java.lang.NullPointerException
       at com.atlassian.seraph.auth.DefaultAuthenticator.getUserFromBasicAuthentication(DefaultAuthenticator.java:501)
   

   And the stacktrace :

   java.lang.NullPointerException
   	at com.atlassian.seraph.auth.DefaultAuthenticator.getUserFromBasicAuthentication(DefaultAuthenticator.java:501)
   	at com.atlassian.seraph.auth.DefaultAuthenticator.getUser(DefaultAuthenticator.java:280)
   	at com.atlassian.confluence.user.ConfluenceAuthenticator.getUser(ConfluenceAuthenticator.java:79)
   	at com.atlassian.seraph.auth.AbstractAuthenticator.getUser(AbstractAuthenticator.java:45)
   	at com.atlassian.seraph.filter.BaseLoginFilter$SecurityHttpRequestWrapper.getUserPrincipal(BaseLoginFilter.java:216)
   	at com.atlassian.seraph.filter.BaseLoginFilter$SecurityHttpRequestWrapper.getRemoteUser(BaseLoginFilter.java:210)
   	at com.atlassian.confluence.util.LoggingContextFilter.doFilter(LoggingContextFilter.java:27)
   	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.confluence.web.filter.ThreadLocalCacheFilter.doFilter(ThreadLocalCacheFilter.java:22)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.confluence.util.UserThreadLocalFilter.doFilter(UserThreadLocalFilter.java:44)
   	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.seraph.filter.SecurityFilter.doFilter(SecurityFilter.java:101)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.confluence.util.AbstractBootstrapHotSwappingFilter$SwapOnBootstrapFilter.doFilter(AbstractBootstrapHotSwappingFilter.java:42)
   	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
   	at com.atlassian.confluence.util.AbstractBootstrapHotSwappingFilter.doFilter(AbstractBootstrapHotSwappingFilter.java:30)
   	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.seraph.filter.BaseLoginFilter.doFilter(BaseLoginFilter.java:140)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:71)
   	at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:63)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.confluence.util.ClusterHeaderFilter.doFilter(ClusterHeaderFilter.java:34)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.johnson.filters.AbstractJohnsonFilter.doFilter(AbstractJohnsonFilter.java:72)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.spring.filter.FlushingSpringSessionInViewFilter.doFilterInternal(FlushingSpringSessionInViewFilter.java:26)
   	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:75)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.confluence.util.ConfluenceErrorFilter.doFilter(ConfluenceErrorFilter.java:22)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.util.profiling.filters.ProfilingFilter.doFilter(ProfilingFilter.java:99)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.confluence.core.datetime.RequestTimeThreadLocalFilter.doFilter(RequestTimeThreadLocalFilter.java:35)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.confluence.util.RequestCacheThreadLocalFilter.doFilter(RequestCacheThreadLocalFilter.java:25)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.gzipfilter.GzipFilter.doFilterInternal(GzipFilter.java:81)
   	at com.atlassian.gzipfilter.GzipFilter.doFilter(GzipFilter.java:51)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.core.filters.cache.AbstractCachingFilter.doFilter(AbstractCachingFilter.java:33)
   	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:71)
   	at com.atlassian.plugin.servlet.filter.ServletFilterModuleContainerFilter.doFilter(ServletFilterModuleContainerFilter.java:63)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.core.filters.encoding.AbstractEncodingFilter.doFilter(AbstractEncodingFilter.java:41)
   	at com.atlassian.core.filters.AbstractHttpFilter.doFilter(AbstractHttpFilter.java:31)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.core.filters.HeaderSanitisingFilter.doFilter(HeaderSanitisingFilter.java:44)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at com.atlassian.confluence.servlet.FourOhFourErrorLoggingFilter.doFilter(FourOhFourErrorLoggingFilter.java:65)
   	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
   	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
   	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
   	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
   	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
   	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
   	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
   	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:263)
   	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
   	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:584)
   	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
   	at java.lang.Thread.run(Thread.java:619)