Migrate Garmin authentication to Garth OAuth fixes #128

[SimonBaars]

Garmin no longer support auth via the former authentication flow. The Garth library implements authentication via OAuth, which is the recommended methods.

I implemented a solution for this problem in related Python repositories:

• Use a Garth OAuth implementation fixes #95 pe-st/garmin-connect-export#96
• Migrate to new auth flow and use Garth, fixes #103 petergardfjall/garminexport#104

For this particular one: I'm personally not a Withings user, so I couldn't end-to-end test the solution. Please test before merging.

For full context, see the relevant issue thread: pe-st/garmin-connect-export#95

Garmin shut down the old authentication flow. The new authentication flow has many security measures in place to script the login. We can use the Garth library to implement an OAuth flow, which should be more robust than the original method.

The OAuth flow also required using the new endpoints (which could be migrated by simply removing the proxy).

Thanks to @geraudloup for investigating this with me, and @app4g for the support!

[stynoo]

Thanks @SimonBaars , this looks like a clean solution (and maybe the key to avoid the upload of identical weight entries).
iirc requirements.txt & setup.py need to be updated as well.

[SimonBaars]

@stynoo Indeed! I committed adding the lib to requirements.txt and setup.py.

[longstone]

Thx, I'll create a release.