The function SimpleOAuth.Internal.SignatureMethod.CreateSignature is not thread-safe

[keltex]

SimpleOAuth.Internal.SignatureMethod.CreateSignature uses an internal static dictionary. So either access to the dictionary should be locked or should be replaced with a ConcurrentDictionary.

[djmc]

I don't maintain this anymore (I haven't actually done any .net development for a few years), but feel free to provide a fix.

[keltex]

Sounds good. I'll do a pull request.