Intial authfile man page

The initial man page for the authfile used by
the container tools.

Fixes: containers/podman#4359

Signed-off-by: TomSweeneyRedHat <tsweeney@redhat.com>

docs/containers-auth.json.5.md

@@ -0,0 +1,43 @@
+% containers-auth.json(5)
+
+# NAME
+containers-auth.json - syntax for the registry authentication file
+
+# DESCRIPTION
+
+A credentials file stored at `${XDG_RUNTIME_DIR}/containers/auth.json` in
+json format used to authenticate against container image registries.
+
+## FORMAT
+
+The auth.json file stores encrypted authentication information for the
+user to container image registries.  The file can have zero to many entries and
+is created by a `login` command from a container tool such as `podman login` or
+`buildah login`.  Each entry includes the name of the registry and then an auth
+token in the form of a base64 encoded string from the concatenation of the
+username, a colon, and the password.
+
+The following example shows the values found in auth.json after the user logged in to
+their accounts on quay.io and docker.io:
+
+```
+{
+	"auths": {
+		"docker.io": {
+			"auth": "erfi7sYi89234xJUqaqxgmzcnQ2rRFWM5aJX0EC="
+		},
+		"quay.io": {
+			"auth": "juQAqGmz5eR1ipzx8Evn6KGdw8fEa1w5MWczmgY="
+		}
+	}
+}
+```
+
+An entry can be removed by using a `logout` command from a container
+tool such as `podman logout` or `buildah logout`.
+
+# SEE ALSO
+    buildah-login(1), buildah-logout(1), podman-login(1), podman-logout(1)
+
+# HISTORY
+Feb 2020, Originally compiled by Tom Sweeney <tsweeney@redhat.com>