Add an implementation of the Pubkey Access Authentication Scheme proposed
by Oliver Gould in

http://www.olix0r.net/PubKeyAccessAuthScheme.txt

This implementation includes an example client and ser

Add an implementation of the Pubkey Access Authentication Scheme proposed
by Oliver Gould in

http://www.olix0r.net/PubKeyAccessAuthScheme.txt

This implementation includes an example client and server program, but
is not (yet) hooked into the build.

To quote from Oliver's RFC:

HTTP services are a core Internet technology, yet the Digest
authentication scheme provided by RFC 2617 only describes
authentication by way of shared-secrets (i.e. passwords).
This model has operational drawbacks, as authenticating
services are required to have access to a user's secret (or a
hash thereof), or retrograde technologies, such as cookies,
are employed.

Similarly to SSH's "publickey" authentication method [RFC
4252], the PubKey Access Authentication scheme allows an HTTP
server to authenticate clients using public key credentials.

Like the Digest Access Authentication Scheme [RFC 2617], the
PubKey.v1 scheme is based on a simple challenge-response
paradigm. The PubKey scheme responds to unauthorized clients
with a challenge value; and a valid response contains a
cryptographic signature of client's id, the authentication
realm, and the server's challenge.

The client's secret never leaves the client. The server
verifies the client's signed authorization request with the
client's published public keys.

libpaa(3) uses libnetpgp(3) for its digital signatures, SHA1Init(3)
for digests, and base64 encoding for transmission of data.

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