OCI: Add an authenticator for OCI remotes

Given a configuration like:

[remote "oci-remote"]
url=oci+http:https://some.server.com/api/v1/organization/foo?index=labels
xa.authenticator-name=org.flatpak.Authenticator.Oci
xa.default-token-type=1
xa.authenticator-options={"auth": <"a-token-here">}

I was able to install an app from an OCI remote that required a login

Makefile.am

@@ -97,6 +97,7 @@ include app/Makefile.am.inc
 include session-helper/Makefile.am.inc
 include portal/Makefile.am.inc
 include system-helper/Makefile.am.inc
+include oci-authenticator/Makefile.am.inc
 include icon-validator/Makefile.am.inc
 include revokefs/Makefile.am.inc
 include selinux/Makefile.am.inc

common/flatpak-oci-registry.c

@@ -983,8 +983,6 @@ flatpak_oci_registry_get_token (FlatpakOciRegistry *self,
 {
  g_autofree char *subpath = NULL;
  g_autoptr(SoupURI) uri = NULL;
- g_autoptr(GBytes) bytes = NULL;
- g_autofree char *uri_s = NULL;
  g_autoptr(GInputStream) stream = NULL;
  g_autoptr(SoupMessage) msg = NULL;
  g_autofree char *www_authenticate = NULL;

oci-authenticator/Makefile.am.inc

@@ -0,0 +1,28 @@
+libexec_PROGRAMS += \
+ flatpak-oci-authenticator \
+ $(NULL)
+
+service_in_files += oci-authenticator/flatpak-oci-authenticator.service.in
+systemduserunit_DATA += oci-authenticator/flatpak-oci-authenticator.service
+
+service_in_files += oci-authenticator/org.flatpak.Authenticator.Oci.service.in
+dbus_service_DATA += oci-authenticator/org.flatpak.Authenticator.Oci.service
+
+flatpak_oci_authenticator_SOURCES = \
+ oci-authenticator/flatpak-oci-authenticator.c \
+ $(NULL)
+
+BUILT_SOURCES += $(nodist_flatpak_oci_authenticator_SOURCES)
+CLEANFILES += $(nodist_flatpak_oci_authenticator_SOURCES)
+
+flatpak_oci_authenticator_LDADD = $(AM_LDADD) $(BASE_LIBS) $(OSTREE_LIBS) libflatpak-common.la libflatpak-common-base.la libglnx.la
+flatpak_oci_authenticator_CFLAGS = \
+ $(AM_CFLAGS) \
+ $(BASE_CFLAGS) \
+ $(OSTREE_CFLAGS) \
+ $(SOUP_CFLAGS) \
+ $(JSON_CFLAGS) \
+ -DFLATPAK_COMPILATION \
+ -DDATADIR=\"$(datadir)\" \
+ $(NULL)
+flatpak_oci_authenticator_CPPFLAGS = $(AM_CPPFLAGS) -I$(builddir)/oci-authenticator