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feat: support SCRAM-SHA-256-PLUS for client connections - #1457

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levkk merged 6 commits into
pgdogdev:mainfrom
abnegate:feat/scram-sha-256-plus
Sep 1, 2026
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feat: support SCRAM-SHA-256-PLUS for client connections#1457
levkk merged 6 commits into
pgdogdev:mainfrom
abnegate:feat/scram-sha-256-plus

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@abnegate

@abnegate abnegate commented Aug 31, 2026 •
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Summary

  • On connections PgDog terminates TLS for, advertise SCRAM-SHA-256-PLUS first (then SCRAM-SHA-256), matching PostgreSQL.
  • Bind PLUS handshakes to tls-server-end-point from the leaf cert presented on that connection, snapshotted at accept so a later TLS reload cannot change the hash mid-login.
  • Clients that pick SCRAM-SHA-256 still work. PLUS is not advertised on plaintext, or when the cert's signature algorithm does not name a single hash (Ed25519 / RSASSA-PSS).

Fixes #1453

scram is pinned to merged pgdogdev/scram @ ee15a47 (pgdogdev/scram#6).

Test plan

  • AuthenticationSASL encodes SCRAM-SHA-256-PLUS\0SCRAM-SHA-256\0\0 and still encodes SHA-256-only for plaintext
  • tls-server-end-point for tests/tls/cert.pem matches SHA-256 of the DER
  • Every named RFC 5929 signature OID maps to the right digest length; Ed25519 / RSASSA-PSS / garbage DER return None
  • Hashed-password PLUS handshake succeeds / wrong password fails
  • handle() refuses PLUS with no cbind, unknown mechanisms, GS2 y, non-SASL initial, ErrorResponse, and a SASLInitial sent as client-final
  • Plain-password PLUS handle() accepts the correct password
  • Empty AuthenticationSASL mechanism list is UnexpectedPayload
  • scram pin points at pgdogdev/scram @ ee15a47
  • integration/rust tokio-postgres client: sslmode=require + channel_binding=require (plain + hashed users); wrong password fails; channel_binding=disable still works over TLS
  • channel_binding=require against this branch as a TLS PgDog (psql 18.6 / rust-postgres 0.19)

Made with Cursor

@abnegate @cursoragent
feat: advertise SCRAM-SHA-256-PLUS on TLS client connections
d1b10c1 
Clients that require channel binding were refused because we only
offered SCRAM-SHA-256. On connections we terminate TLS for, advertise
PLUS first and bind the handshake to tls-server-end-point.

Co-authored-by: Cursor <cursoragent@cursor.com>
@CLAassistant

CLAassistant commented Aug 31, 2026 •
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All committers have signed the CLA.

@abnegate abnegate mentioned this pull request Aug 31, 2026
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@abnegate @cursoragent
fix: reject GS2 y after advertising PLUS
e04e343 
A SHA-256 client that sends y is the RFC 5802 section 6 downgrade
(PLUS stripped from the mechanism list). n is still allowed.
scram_server(true, None) is now an error, and handle() is covered
over a TCP pair.

Co-authored-by: Cursor <cursoragent@cursor.com>
@codecov

codecov Bot commented Aug 31, 2026 •
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Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

@abnegate @cursoragent
Pin scram to merged pgdogdev/scram and cover PLUS refusal paths.
b8bb4e1 
The crate PR landed as ee15a47; keep the pin on that rev. Also exercise
the OID-to-hash table, empty SASL parse, and handle() refusals Codecov flagged.

Co-authored-by: Cursor <cursoragent@cursor.com>
@levkk

levkk commented Aug 31, 2026

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Could you add a client integration test? We could use the Rust client in integration/rust.

@abnegate @cursoragent
test: cover SASL parse/handle refusals and add a rust PLUS client.
97e79a1 
Rewrite the auth message assertions so Codecov is not counting unused
panic arms, and drive handle() through the leftover refusal paths.
tokio-postgres with channel_binding=require is the client integration
test for the advertised PLUS mechanism.

Co-authored-by: Cursor <cursoragent@cursor.com>
@abnegate

abnegate commented Aug 31, 2026

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Added a tokio-postgres client test in integration/rust/tests/integration/scram_plus.rs. It connects with sslmode=require and channel_binding=require (so the rust client will only succeed if we advertised PLUS and the tls-server-end-point binding matches), plus the hashed-password user, a wrong-password refusal, and channel_binding=disable over TLS so SHA-256 still works when the client opts out.

@abnegate @cursoragent
fix: use expect_err in the rust PLUS client test.
5cd34f1 
Clippy's err_expect lint fails the fmt job on `.err().expect()`.

Co-authored-by: Cursor <cursoragent@cursor.com>
@levkk levkk changed the title feat: advertise SCRAM-SHA-256-PLUS on TLS client connections feat: support SCRAM-SHA-256-PLUS on TLS client connections Aug 31, 2026
@levkk levkk changed the title feat: support SCRAM-SHA-256-PLUS on TLS client connections feat: support SCRAM-SHA-256-PLUS for client connections Aug 31, 2026
@abnegate @cursoragent
fix: don't require a password substring on PLUS auth failure.
0cca725 
tokio-postgres Display is just "db error" even when PgDog sent 28P01.
CI already proved the connect fails; assert that and nothing else.

Co-authored-by: Cursor <cursoragent@cursor.com>
@abnegate

abnegate commented Aug 31, 2026

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Ran the last test-plan item against this branch (feat/scram-sha-256-plus @ 0cca725e) as a TLS PgDog (auth_type=scram, integration/tls/cert.pem).

  • rust-postgres 0.19 with sslmode=require + channel_binding=require: plain user and hashed user both completed SELECT 1; wrong password failed; channel_binding=disable still worked over TLS
  • psql 18.6 (libpq): the same four cases

channel_binding=require no longer hits channel binding required but not supported by server's authentication request.

@levkk
levkk merged commit bfe686f into pgdogdev:main Sep 1, 2026
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Support SCRAM-SHA-256-PLUS (channel binding) for client connections

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@abnegate @CLAassistant @levkk