How to call Google Fit APIs with the user's JWT?

Question

I am trying to make a simple ReactJS webapp where I can fetch for example the authenticated user's steps.

I'm using React OAuth2 | Google for the authentication and I can successfully get the user's JWT.

<GoogleLogin
          onSuccess={credentialResponse => {
            console.log(credentialResponse);
            setUser(credentialResponse);
          }}
          onError={() => {
            console.log('Login Failed');
          }}
        />
      )}
</GoogleOAuthProvider>

But now I'am at loss. I'm simply trying to call an endpoint with the JWT but I only get 401. I understand I should use an access token instead but since Google has moved to the new Google Identity Services, I have no idea how to get an access token from JWT, or use the JWT to authenticate and call these endpoints.

 axios
          .get(GOOGLE_FIT_ENDPOINT, {
            headers: {
              Authorization: `Bearer ${user.credential}`,
              Accept: 'application/json'
            }
          })
          .then((res) => {
            setProfile(res.data);
          })
          .catch((err) => console.log(err));

Since it's new, I could not find any documentation or tutorial about it.

All I could find was how to get the JWT token, or how to call a Google API endpoint with access or refresh token. But there must be a step in the middle I'm missing.

FIY, I also set up a Express JS server as a backend.

Could anyone point me out to the right direction please?