Freeipa: ipa: idm: freeipa: off-by-one buffer overflows in ipa-otpd oauth2.c during oauth2 device authorization

Two off-by-one errors in the FreeIPA ipa-otpd daemon's OAuth2 device authorization handler can cause out-of-bounds memory access when processing an oversized response from a configured external OAuth2/OIDC Identity Provider. An attacker who controls or can man-in-the-middle the IdP endpoint may be able to trigger ipa-otpd to write or read one byte past the end of a fixed-size buffer. Exploitation requires FreeIPA to be configured with an external IdP, attacker control or MITM of that IdP, and a user to initiate the OAuth2 device authorization flow. The most likely impact is limited denial of service affecting the ipa-otpd daemon.