How to get user data/authenticate with bearer token - Simple OAuth - Decoupled
I'm not familiar with the Nuxtjs framework discussed in the tutorial you linked to, but basically once you have the access_token the user should be authenticated in Drupal. It should be enough that you on each request set an Authorization header that contains that access token, as described in the tutorial:

this.$axios.setHeader('Authorization', 'Bearer ' + resp.data.access_token)


Drupal will then read the Authorization header value and authenticate/authorize the user based on the Drupal role that the user has assigned to itself. So provided you have the REST endpoints for user information active you should be able to make a GET request to /user/{user} and get the logged in user information.

You can try this out using curl or Postman by manually adding the header to the request:

Authorization: Bearer HereGoesTheValueOfTheAccessToken


A curl example:

curl --request GET \
  --url https://mydrupaldomain.com/user/123 \
  --header 'authorization: Bearer HereGoesTheValueOfTheAccessToken'