Protocol between the server and the clients
===========================================

Messages are sent through a UNIX-domain sequential packet socket
and authenticated by automatic passing of user credentials.
For every request, a reply is sent through the same connection.
Pipelining of requests is currently not supported.

All requests and replies are serialized as JSON objects. Requests
have always the "cmd" attribute set to the name of the command.
Replies always have the "error" attribute set; it contains an error
message or an empty string to indicate success.

Some operations require root privileges. Other operations are
unprivileged if no login name present, or if it matches the UID
of the requesting user.

# No operation (unprivileged)
{
	"cmd": "nop"
}

# Create an account (privileged)
{
	"cmd": "create-acct",
	"login": "login name",
	"zone": "auth zone"
}

# Delete an account (privileged)
{
	"cmd": "delete-acct",
	"login": "login name",
	"zone": "auth zone"		# "*" to delete accounts in all zones
}

# Create an authentication token
{
	"cmd": "create-token",
	"login": "login name",
	"zone": "auth zone",
	"comment": "optional comment"
}
{
	"error": "",
	"token": "new token",
	"ident": "token id"
}

# Delete an authentication token
{
	"cmd": "delete-token",
	"login": "login name",
	"zone": "auth zone",
	"ident": "token id"			# "*" for all tokens for the login+zone
}

# Change parameters of a token
{
	"cmd": "change-token"
	"login": "login name",
	"zone": "auth zone",
	"ident": "token id",
	"comment": "new comment"		# optional
}

# Set password for an account
{
	"cmd": "set-passwd",
	"login": "login name",
	"zone": "auth zone",
	"passwd": "new password"
}

# Delete password for an account
{
	"cmd": "delete-passwd",
	"login": "login name",
	"zone": "auth zone"
}

# Create a temporary token
{
	"cmd": "create-temp",
	"login": "login name",
	"zone": "auth zone",
	"validity": seconds		# Requested token validity
}
{
	"error": "",
	"token": "new token"
}

# Authenticate a user
{
	"cmd": "login",
	"login": "login name",
	"zone": "auth zone",
	"passwd": "password or token"
}

# List user's accounts and tokens
{
	"cmd": "list-accts",
	"login": "login name",
}
{
	"error": "",
	"login: "login name",
	"accounts": [
		{
			"zone": "auth zone",
			"tokens": [
				{
					"type": "token type",	# passwd/token
					"ident": "token id",
					"lastmod": timestamp	# UNIX timestamp of last modification
				}
				...
			]
		}
		...
	]
}

# List known authentication zones
{
	"cmd": "list-zones"
}
{
	"error": "",
	"zones": [
		{
			"name": "auth zone",
			"desc": "human-readable description",
			"allow-passwd": integer,		# Does the zone support passwords?
			"allow-tokens": integer,		# Does the zone support auth tokens?
			"max-temp-validity": seconds		# Maximum validity of temp tokens
								# (if no temp tokens supported)
		}
		...
	]
}