Unable to use proxy which requires authentication

In our environment we need to access an oidc1.0 identity provider over our corporate proxy.
This proxy requires authentication.
I have configured the proxy like so:

jobs:
  - name: uaa
     properties:
       env:
         http_proxy: http://user:password@example.com:8080

but I get the following error:

[2017-12-21 14:15:24.977] uaa - 23341 [https-jsse-nio-8443-exec-4] ....  WARN --- ExpiringUrlCache: Unable to fetch metadata for https://idp.example.com/openid-configuration
org.springframework.web.client.ResourceAccessException: I/O error on GET request for "https://idp.example.com/openid-configuration": user: Name or service not known; nested exception is java.net.UnknownHostException: user: Name or service not known
        at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:666)
        at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:628)
        at org.springframework.web.client.RestTemplate.getForObject(RestTemplate.java:303)
        at org.cloudfoundry.identity.uaa.cache.ExpiringUrlCache.getUrlContent(ExpiringUrlCache.java:62)
        at org.cloudfoundry.identity.uaa.provider.oauth.XOAuthProviderConfigurator.overlay(XOAuthProviderConfigurator.java:67)
        at org.cloudfoundry.identity.uaa.provider.oauth.XOAuthProviderConfigurator.lambda$retrieveAll$2(XOAuthProviderConfigurator.java:167)
        at java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:184)
        at java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:175)
        at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382)
        at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
        at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
        at java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:151)
        at java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:174)
        at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
        at java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:418)
        at org.cloudfoundry.identity.uaa.provider.oauth.XOAuthProviderConfigurator.retrieveAll(XOAuthProviderConfigurator.java:164)
        at org.cloudfoundry.identity.uaa.login.LoginInfoEndpoint.getOauthIdentityProviderDefinitions(LoginInfoEndpoint.java:525)
        at org.cloudfoundry.identity.uaa.login.LoginInfoEndpoint.login(LoginInfoEndpoint.java:315)
        at org.cloudfoundry.identity.uaa.login.LoginInfoEndpoint.loginForHtml(LoginInfoEndpoint.java:267)
        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:498)

I think it breaks here since the : gets replace by a space.

Start by reading jobs/uaa/templates/bin/configure_proxy.erb around line 21 and compare it with the authenticated proxy URL and UnknownHostException shown here. Reproduce the metadata request through an authenticated proxy; done when the configured proxy preserves the credentials and the oidc1.0 metadata can be fetched without that error.