Add GitHub OIDC to Fulcio (#181)

Signed-off-by: Dan Lorenc <dlorenc@google.com>

config/fulcio-config.yaml

@@ -31,6 +31,11 @@ data:
               "IssuerURL": "https://oidc.dlorenc.dev",
               "ClientID": "sigstore",
               "Type": "spiffe"
+            },
+            "https://vstoken.actions.githubusercontent.com": {
+              "IssuerURL": "https://vstoken.actions.githubusercontent.com",
+              "ClientID": "sigstore",
+              "Type": "github-workflow"
             }
           }
         }

federation/vstoken.actions.githubusercontent.com/config.yaml

@@ -0,0 +1,18 @@
+# Copyright 2021 The Sigstore Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+url: https://vstoken.actions.githubusercontent.com
+contact: support@sigstore.dev
+description: "github actions OIDC auth"
+type: "github-workflow"