Concurrency problems with shared client context

[dkocher]

Currently because the client HttpContext ¹ is shared across executions of different requests there is a concurrency issue as the context should not be considered thread safe.

IMPORTANT: Please note HTTP context implementation, even when thread safe, may not be used concurrently by multiple threads, as the context may contain thread unsafe attributes. ²

This can cause issues with the authentication state (http.auth.target-scope) used in the request execution phase and user token (http.user-token) used to determine connection reuse from the pool. Both properties are stored in the context.

Relates to ³.

Footnotes

1. https://github.com/lookfirst/sardine/blob/master/src/main/java/com/github/sardine/impl/SardineImpl.java#L169 ↩

2. https://hc.apache.org/httpcomponents-core-4.4.x/current/httpcore/apidocs/org/apache/http/protocol/HttpContext.html ↩

3. Unexpected 401 when using SharePoint WebDav NTLM authentication iterate-ch/cyberduck#15127 ↩

[dkocher]

Previously in #265 that does not cover all cases.