update permission headers to allow explicit null

use enum instead of boolean for explicit serialisation

Author: pdowler

openapi/vosi/vosi-auth-read.yaml

@@ -1,8 +1,9 @@
 # request header
 name: x-vosi-auth-read
 in: header
-description: flag indicating that the resource cannot be read with an anonymous request
+description: flag indicating that the resource requires authentication to read
 required: false
 schema:
-  type: boolean
+  type: string
+  enum: ["true", "false", "null"]
 

openapi/vosi/vosi-group-read.yaml

@@ -1,7 +1,10 @@
 # request header
 name: x-vosi-group-read
 in: header
-description: a GMS group identifier indicating a group with read permission
+description: a GMS group identifier indicating a group with read permission, or literal null
 required: false
 schema:
-  type: string
+  oneOf:
+    - type: string
+      format: uri
+    - type: "null"

openapi/vosi/vosi-group-write.yaml

@@ -1,7 +1,10 @@
 # request header
 name: x-vosi-group-write
 in: header
-description: a GMS group identifier indicating a group with write permission
+description: a GMS group identifier indicating a group with write permission, or literal null
 required: false
 schema:
-  type: string
+  oneOf:
+    - type: string
+      format: uri
+    - type: "null"

openapi/vosi/vosi-table.yaml

@@ -122,10 +122,11 @@ components:
             description: metadata for the specified schema or table
             headers:
               x-vosi-auth-read:
-                description: flag indicating that the resource allows anonymous read
+                description: flag indicating that the resource requires authentication to read
                 required: false
                 schema:
-                  type: boolean
+                  type: string
+                  enum: ["true", "false"]
               x-vosi-group-read:
                 description: a GMS group identifier indicating a group with read permission
                 required: false