/*STRAVA_API

OAuth2.0 strava / pebble

1 - get activity:write authorization (once and for all)
    GET https://www.strava.com/oauth/authorize?client_id=94880&response_type=code&redirect_uri=http://strava.jonget.fr&approval_prompt=force&state=bike_companion&scope=activity:write
    monitor state, code and scope (as upload can be unchecked)!
    code is short lived and one time usage
2 - get tokens in exchange of code (make it done by jonget.fr because of secret ? )
    POST https://www.strava.com/oauth/token?client_id=94880&client_secret=08dc170f0fe38f39dd327bea82a28db4400e6f00&code=db896b06f89804997a8088320fba755e6299c0d6&grant_type=authorization_code
    refresh & access tokens + expiry of access token (6hours) retrieved

3 - test if access token expired

4a- if not, API call
    GET https://www.strava.com/api/v3/athlete with "Authorization" header ="Bearer XXXXX"  XXXXX=access token

4b- if yes refresh access token with refresh token get in 2  (make it done by jonget.fr because of secret ? )
    POST https://www.strava.com/oauth/token?client_id=94880&client_secret=8a68d5b79f2fb3e00ad3eaa5025253990fbd6a58&refresh_token=c313d612768db4b12af2782372aa1d9349c265cb&grant_type=refresh_token
*/