fix(tokenExchange): use correct token type for userInfo requests

[0x0dr1y]

Overview

This small changes fixes an issue in the token exchange flow. It explicitly sets the tokenType used for GET /userinfo to Bearer to be conform with the OIDC spec.

What this PR does / why we need it

Without this change the tokenType would be set to either urn:ietf:params:oauth:token-type:access_token or urn:ietf:params:oauth:token-type:id_token, which doesn't satisfy the OIDC spec.

The Access Token obtained from an OpenID Connect Authentication Request MUST be sent as a Bearer Token, per Section 2 of OAuth 2.0 Bearer Token Usage [RFC6750].

https://openid.net/specs/openid-connect-core-1_0.html#UserInfo (5.3.1)

Closes #3335

[nabokihms]

@MrDeerly thanks! It does make sense. Because there are no integration tests, I will test this PR manually. If everything is okay, I will bump the merge button.

[nabokihms]

Tested it and it works as expected, so, LGTM! Thank you for the fix.