Define a default CredentialsProvider

This permits applications to set their preferred credentials UI
implementation once, rather than needing to define it on every
single Transport instance they open.

Change-Id: I010550de1a6becab27f7aa5a9901df5a1c7e74bd
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
2 files changed