Add initial authentication for OpenAPI

Currently only contains basic auth definitions to keep it simple stupid.
Mostly just following https://swagger.io/docs/specification/v3_0/authentication/basic-authentication/

api/openapi/authentication.yaml

@@ -0,0 +1,28 @@
+openapi: 3.0.3
+info:
+  title: FabAccess Auth API
+  version: 0.0.1
+
+paths: {}
+
+components:
+  responses:
+    Unauthorized:
+      description: Authentication information is missing or invalid
+      headers:
+        WWW_Authenticate:
+          schema:
+            $ref: '#/components/schemas/AuthenticationMethod'
+
+  schemas:
+    AuthenticationMethod:
+      type: string
+      description: Mechanism for authentication
+
+  securitySchemes:
+    basicAuth:
+      type: http
+      scheme: basic
+
+security:
+- basicAuth: []