oauth: allow using templates in OAuth response template

airbyte has recently introduced new fields to their OAuth response
mappings, which need processing. In this case, we have AirTable which
requires the `expires_in` field of response to be added to `now()` and
rendered as an RFC3339 date to work. So I'm adding a condition here
which allows response map to be rendered using a template instead of
just jsonpointer.

In hindsight, we can probably just get rid of jsonpointers here and use
mustache templates for the responseMap since it can do the same job
anyway. For now I'm keeping both.

supabase/functions/_shared/helpers.ts

@@ -22,6 +22,15 @@ export const mustacheHelpers = {
         return btoa(render(s));
       }
     },
+    now_plus: function(s: any) {
+      return (s: string, render: any) => {
+        const now = new Date();
+        const inputSeconds = parseInt(render(s))
+        const newDate = new Date(now + inputSeconds * 1000)
+
+        return newDate.toISOString()
+      }
+    }
 };
 
 export const compileTemplate = (template: string, data: any, connector_id: string) => {

supabase/functions/oauth/access-token.ts

@@ -114,7 +114,11 @@ export async function accessToken(req: Record<string, any>) {
 
     let mappedData: Record<string, any> = {};
     for (const key in accessTokenResponseMap) {
-        mappedData[key] = jsonpointer.get(responseData, accessTokenResponseMap[key]);
+        if (accessTokenResponseMap[key].startsWith('/')) {
+          mappedData[key] = jsonpointer.get(responseData, accessTokenResponseMap[key]);
+        } else {
+          mappedData[key] = compileTemplate(accessTokenResponseMap[key], responseData);
+        }
     }
 
     return new Response(JSON.stringify(mappedData), {