Need a way to deal with proxy servers that return 200 with error pages.

It is fairly common for larger sites to have proxy servers which redirect to an error page when something goes wrong in an HTTP request. This can cause invalid artifacts to be stored in proxy repositories, since the redirect URL usually returns 200 or similar.

Depending on the server it may not be possible to change this behavior, and the obvious workaround of enabling strict checksums isn't always feasible because not all remote repositories have valid checksums for all artifacts.

We should provide a workaround for users who find themselves in this situation.

One possibility would be to check for some information in the http headers to indicate to nexus that the artifact should not be cached.

Another thought: A"valid checksum" mode, where nexus requests the checksum file but only checks to see that it has a valid format. If a checksum is received with non-error response and it isn't in valid format the artifact would be rejected.