Add support for bearer/token auth

New options added to configuration file to reference a public key used
to validate authorization tokens signed by an auth server with
corresponding private key.

Resolves #24

Signed-off-by: Peter Engelbert <pmengelbert@gmail.com>

WORKSPACE

@@ -134,6 +134,13 @@ go_repository(
     version = "v1.1.0",
 )
 
+go_repository(
+    name = "com_github_chartmuseum_auth",
+    importpath = "github.com/chartmuseum/auth",
+    sum = "h1:76rqyKtBdQAnC/YuT9ftL7OpLTDwfrfk8Ee8rD9OVOw=",
+    version = "v0.3.1",
+)
+
 go_repository(
     name = "com_github_client9_misspell",
     importpath = "github.com/client9/misspell",
@@ -1051,6 +1058,13 @@ go_repository(
     version = "v0.0.0-20170223121919-b73f66626b33",
 )
 
+go_repository(
+    name = "com_github_mitchellh_mapstructure",
+    importpath = "github.com/mitchellh/mapstructure",
+    sum = "h1:fmNYVwqnSfB9mZU6OS2O6GsXM+wcskZDuKQzvN1EDeE=",
+    version = "v1.1.2",
+)
+
 go_repository(
     name = "com_github_nmcclain_asn1_ber",
     importpath = "github.com/nmcclain/asn1-ber",
@@ -1072,6 +1086,13 @@ go_repository(
     version = "v0.0.0-20160315200505-970db520ece7",
 )
 
+go_repository(
+    name = "com_github_opencontainers_go_digest",
+    importpath = "github.com/opencontainers/go-digest",
+    sum = "h1:WzifXhOVOEOuFYOJAW6aQqW0TooG2iki3E3Ii+WN7gQ=",
+    version = "v1.0.0-rc1",
+)
+
 go_repository(
     name = "com_github_phayes_freeport",
     importpath = "github.com/phayes/freeport",