rfc2865: add CHAP password verification helpers#143
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rfc2865 exposed accessors for the CHAP-Password and CHAP-Challenge attributes but no way to verify a CHAP (RFC 1994 / RFC 2865) response against a known password. MS-CHAP and MS-CHAPv2 helpers already exist in rfc2759, but plain CHAP did not, so servers handling equipment that uses standard CHAP (for example some Huawei switches) had to implement the MD5 check themselves. Add CHAPMatch, which checks a raw CHAP-Password value against a password and challenge in constant time, and CHAPVerify, a packet-level convenience that pulls the CHAP-Password and CHAP-Challenge attributes (falling back to the packet Authenticator as the challenge, per RFC 2865, Section 2.2). Closes layeh#96 Co-authored-by: Copilot <[email protected]>
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Summary
rfc2865exposedCHAPPasswordandCHAPChallengeaccessors but offered no way to actually verify a CHAP login (plain CHAP, not MS-CHAP). This adds the missing helper, mirroring the hand-written helper style already used byrfc2759(MS-CHAPv2).CHAP verification per RFC 2865 §2.2:
CHAP-Passwordvalue isCHAP-Identifier || MD5(CHAP-Identifier || password || challenge), where the challenge is theCHAP-Challengeattribute if present, otherwise the Request Authenticator.API
Both use
crypto/subtle.ConstantTimeCompare.CHAPVerifyfalls back to the packet Authenticator when noCHAP-Challengeattribute is present.Changes
rfc2865/chap.go(new):CHAPMatch,CHAPVerify.rfc2865/chap_test.go(new): match, with-challenge, authenticator-as-challenge, and missing-attribute cases.The generated
rfc2865/generated.gois untouched;go generateonly rewrites that file.Closes #96