I recently encountered an issue where adding basic authentication to some HTTP calls was breaking a Python application.
Come to find out there is a bug in Python 2.6 that appends a newline character to base 64 encoded strings. That newline character then causes your HTTP request to be malformed, so that the body does not match the content length. When consuming these malformed requests in an ASP.NET sever the body content would cut off early, and in the case of JSON content this made it so that the JSON string was incomplete and could not be parsed.
So what's the fix? You can either update Python, or fix your string after encoding.