CVE-2026-101023: Gitea OAuth2 refresh token grant accepts access tokens

Gitea's OAuth2 token endpoint verified the signature and grant of a token submitted with the refreshtoken grant type, but not that the token was a refresh token. An unexpired access token for the same OAuth2 application and grant could be exchanged for a new access token and refresh token. Whoever holds such an access token could keep access beyond the token's original lifetime.