Extend 'transformRequest' to accept an async function callback

[dannyleech]

The problem
I'm using a tile service that requires a short lived OAUTH token. My preferred approach would be to validate the token on each request. If the token has expired then use async await functionality to get a new token before completing the request/
I would expect transformRequest to accept and async function but I understand it doesn't.

My current workaround
Maintain a reference to the token and run a timer to update this just before it expires. However this appears quite fragile for several reasons:

• If the device goes to sleep, or I hide the browser window or tab the timer can stop. When the browser wakes again the token may be invalid. Panning the map then generates a console error. The only fix appears to be to refreshing the browser.
• The timer needs to run whether I'm making a request or not rather than running on demand so not as efficient

Is there an alternative approach to address these issues or would an async transformRequest function be an idea worth exploring?

[HarelM]

You could probably use addProtocol but I'm not sure this is the best approach.
Feel free to take a stab at it.

[dannyleech]

Thanks Harel, ' addProtocol' is a great tip, I imagine steps would be as follows

1. Use transformRequest to intercept https style urls and rewrite them using a custom url schema so that they can be intercepted with addProtocol
2. Use addProtocol to intercept the new custom url and benefit from its async functionality
3. Check token validity and if expired refresh using async await
4. Rewrite custom url back to https and append header with token
5. Use fetch api to get resource and return

This looks like the best work around as it addresses both points above. But as you say perhaps a modification to transformRequest would make sense. I'm not familiar with the code base at all but will endeavour to take a look.

Thanks again for this excellent suggestion!