Flow

1. Create a Fintecture account
2. Register a client application and get the credentials (i.e the app_id) associated to it
3. Request the AIS Connect URL to which you will redirect the user
4. On redirection extract the code received
5. Encode your credentials using Base64 (Basic base64({app_id}:{app_secret})) to generate the Authorization header
6. Exchange the code for an access token using the ais scope and the Authorization header
7. Extract the access_token
8. Use the access_token for every bank account endpoint requiring Bearer
9. Check regularly expires_in and before access token's expiration, ask for a new one and refresh token when needed