Use schema 'id' as a locator for schema registration and performing lookups in the component registry

Author: MaggieKimani1

src/Microsoft.OpenApi/Models/OpenApiDocument.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
+// Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license.
 
 using System;
@@ -529,15 +529,22 @@ internal IOpenApiReferenceable ResolveReference(OpenApiReference reference, bool
             }
 
             string uriLocation;
-            string relativePath = OpenApiConstants.ComponentsSegment + reference.Type.GetDisplayName() + "/" + reference.Id;
+            if (reference.Id.Contains("/")) // this means its a URL reference
+            {
+                uriLocation = reference.Id;
+            }
+            else
+            {
+                string relativePath = OpenApiConstants.ComponentsSegment + reference.Type.GetDisplayName() + "/" + reference.Id;
 
-            uriLocation = useExternal
-                ? Workspace.GetDocumentId(reference.ExternalResource)?.OriginalString + relativePath
-                : BaseUri + relativePath;
+                uriLocation = useExternal
+                    ? Workspace.GetDocumentId(reference.ExternalResource)?.OriginalString + relativePath
+                    : BaseUri + relativePath;
+            }
 
             return Workspace.ResolveReference<IOpenApiReferenceable>(uriLocation);
         }
-                
+
         /// <summary>
         /// Parses a local file path or Url into an Open API document.
         /// </summary>

src/Microsoft.OpenApi/Reader/V31/OpenApiV31Deserializer.cs

@@ -147,11 +147,19 @@ private static string LoadString(ParseNode node)
 
         private static (string, string) GetReferenceIdAndExternalResource(string pointer)
         {
+            /* Check whether the reference pointer is a URL
+             * (id keyword allows you to supply a URL for the schema as a target for referencing)
+             * E.g. $ref: 'https://example.com/schemas/resource.json' 
+             * or its a normal json pointer fragment syntax
+             * E.g. $ref: '#/components/schemas/pet'
+             */
             var refSegments = pointer.Split('/');
-            var refId = refSegments.Last();
-            var isExternalResource = !refSegments.First().StartsWith("#");
+            string refId = !pointer.Contains('#') ? pointer : refSegments.Last();
 
-            string externalResource = isExternalResource ? $"{refSegments.First()}/{refSegments[1].TrimEnd('#')}" : null;
+            var isExternalResource = !refSegments.First().StartsWith("#");
+            string externalResource = isExternalResource
+                ? $"{refSegments.First()}/{refSegments[1].TrimEnd('#')}"
+                : null;
 
             return (refId, externalResource);
         }

src/Microsoft.OpenApi/Services/OpenApiComponentsRegistryExtensions.cs

@@ -20,7 +20,7 @@ public static void RegisterComponents(this OpenApiWorkspace workspace, OpenApiDo
             {
                 if (item.Value.Id != null)
                 {
-                    location = document.BaseUri + item.Value.Id;
+                    location = item.Value.Id;
                 }
                 else
                 {