scripts: add call-context helper for dealing with auth

The call context header used for authentication is base64 encoded,
so it is not practical to generate header values manually, which is
annoying when trying to test the API with tools such as curl.

Add a tiny helper script for development to improve testability.
It can be used with curl as in example:

    curl \
      -H "X-RhApiPlatform-CallContext: $(scripts/call-context some-role)" \
      http://localhost:8080/some/url

scripts/call-context

@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+#
+# Generate a call context header appropriate for authorizing a request with arbitrary
+# exodus-gw roles. This helper script may be used during development to simplify the
+# process of issuing requests from the command line. As the call context header uses
+# base64 encoding, it is not practical to generate header values by hand.
+#
+# Usage:
+#
+#   scripts/call-context role1 role2 ...
+#
+# Example using curl to make a request with "qa-blob-viewer" role:
+#
+#   curl \
+#     -H "X-RhApiPlatform-CallContext: $(scripts/call-context qa-blob-viewer)" \
+#     http://localhost:8080/qa/blobs/a1b2c3
+#
+
+import base64
+import json
+import sys
+
+raw_context = {
+    "user": {
+        "authenticated": True,
+        "internalUsername": "fake-user",
+        "roles": sys.argv[1:],
+    }
+}
+
+json_context = json.dumps(raw_context).encode("utf-8")
+b64_context = base64.b64encode(json_context)
+print(b64_context.decode("utf-8"))