Introduce CustomHosts option

[nikithauc]

Certain workloads error out when an unexpected header is present in the request.

Example -

In case of LargeFileUploadTask in JS library, the upload is as follows:

client.api("UPLOAD_URL").put(chunk_to_be_uploaded)

The middleware appends request headers which are meant for the Graph API.

• When I tried uploading to Outlook, an error was caused because of Authorization header.
• LargeFileUploadTask upload to OneDrive caused cors issue due sdkversion telemetry header

The solution for this is to add a check if the request URL is a Graph endpoint and not send headers to UPLOAD_URL.

Adding the headers only for Graph endpoints ignores the case where the developer might have their own test endpoints.
Example -
MGT uses a proxy sandbox environment
or

Support Custom Graph Endpoint graph.microsoft-ppe.com

microsoftgraph/microsoft-graph-toolkit#1053

I had a conversation with @darrelmiller about handling this case and he proposed that we allow developers to provide custom endpoints and update our conditions to modify request headers.

[MIchaelMainer]

I think we apply retry-count header so we should add the retry handler to this.

As a global comment, lets add a change table at the bottom of these changed spec pages with date and a description of the change so that we can track the changes to spec over time without having to look at the commit history. This way, an SDK owner can understand at a glance whether there are new changes to a spec.

[MIchaelMainer]

Enable a developer provide custom URLs or endpoints.
Enable a developer to provide custom URLs or endpoints.

I think we should consider using the RequestContext mechanism to pass through the CustomUrls option through the middleware, in addition to an on individual request option where we can disable applying our headers.

Should this only be applicable to our default middleware or should the mechanism be accessible to custom middleware? Ideally custom middleware should be able to take advantage of this.

Do you have an example of a workload failing with an unexpected header? I can only think of OneDrive on redirection to a download/upload URL.

[nikithauc]

An example of a workload failing with an unexpected header - I got this error with Outlook large file upload too.

[andrueastman]

If we can, I think it would be great to add a code sample to demonstrate how the CustomURLs options will be used to be able to assess if this will affect the developer experience of the SDK user in any way.

[baywet]

Minor things but besides those, LGTM

[baywet]

Suggested change

	- These URLs are different from the Graph service endpoints on the national clouds.
	- These hostnames are different from the Graph service endpoints on the national clouds.

[baywet]

Suggested change

	- Provide capabilities to modify or update the `CustomURLs` option after the client creation.
	- Provide capabilities to modify or update the `CustomHosts` option after the client creation.