post https://api-sandbox.fintecture.com/oauth/accesstoken
The access token API endpoint is used to get an access token. It enables the TPP to authenticate to the Fintecture Authentication Server.
There are 2 types of grant_types, authorization_code and client_credentials, depending if you require
access to the AIS or PIS resources respectively.
In case of an AIS scope it is provided in exchange to the code received in the /authorize endpoint. For the PIS one, it will be granted according to client credentials.
Once provided, validity of access token is 1h.