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fix: fail-closed expiry enforcement in verify_hmac_and_expiry #176

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Merged
brendanjryan merged 3 commits into from
Apr 7, 2026
+227 −23
Merged

fix: fail-closed expiry enforcement in verify_hmac_and_expiry #176

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f0d4f31
fix: fail-closed expiry enforcement in verify_hmac_and_expiry
brendanjryan Mar 30, 2026
b1caf6a
test: add session path expiry enforcement tests
brendanjryan Mar 30, 2026
a0abade
chore: add changelog entry
brendanjryan Mar 30, 2026
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5 changes: 5 additions & 0 deletions .changelog/fail-closed-expiry.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,5 @@
---
mpp: patch
---

Enforced fail-closed behavior for the `expires` field in `verify_hmac_and_expiry`. Credentials missing the `expires` field are now rejected with a `CredentialMismatch` error instead of being silently accepted. Session challenges now include a default expiry.
245 changes: 222 additions & 23 deletions src/server/mpp.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -237,21 +237,22 @@ where
));
}

if let Some(ref expires) = credential.challenge.expires {
if let Ok(expires_at) =
time::OffsetDateTime::parse(expires, &time::format_description::well_known::Rfc3339)
{
if expires_at <= time::OffsetDateTime::now_utc() {
return Err(VerificationError::expired(format!(
"Challenge expired at {}",
expires
)));
}
} else {
return Err(VerificationError::new(
"Invalid expires timestamp in challenge",
));
}
let expires = credential.challenge.expires.as_deref().ok_or_else(|| {
VerificationError::with_code(
"Challenge missing required expires field",
crate::protocol::traits::ErrorCode::CredentialMismatch,
)
})?;

let expires_at =
time::OffsetDateTime::parse(expires, &time::format_description::well_known::Rfc3339)
.map_err(|_| VerificationError::new("Invalid expires timestamp in challenge"))?;

if expires_at <= time::OffsetDateTime::now_utc() {
return Err(VerificationError::expired(format!(
"Challenge expired at {}",
expires
)));
}

Ok(())
Expand Down Expand Up @@ -485,6 +486,7 @@ where
recipient: &str,
) -> crate::error::Result<PaymentChallenge> {
use crate::protocol::intents::SessionRequest;
use time::{Duration, OffsetDateTime};

let request = SessionRequest {
amount: amount.to_string(),
Expand All @@ -494,13 +496,25 @@ where
};
let encoded = crate::protocol::core::Base64UrlJson::from_typed(&request)?;

let expires = {
let expiry_time = OffsetDateTime::now_utc()
+ Duration::minutes(
crate::protocol::methods::tempo::DEFAULT_EXPIRES_MINUTES as i64,
);
expiry_time
.format(&time::format_description::well_known::Rfc3339)
.map_err(|e| {
crate::error::MppError::InvalidConfig(format!("failed to format expires: {e}"))
})?
};

let id = crate::protocol::methods::tempo::generate_challenge_id(
&self.secret_key,
&self.realm,
"tempo",
"session",
encoded.raw(),
None,
Some(&expires),
None,
None,
);
Expand All @@ -511,7 +525,7 @@ where
method: "tempo".into(),
intent: "session".into(),
request: encoded,
expires: None,
expires: Some(expires),
description: None,
digest: None,
opaque: None,
Expand Down Expand Up @@ -549,6 +563,7 @@ where
options: super::SessionChallengeOptions<'_>,
) -> crate::error::Result<PaymentChallenge> {
use crate::protocol::intents::SessionRequest;
use time::{Duration, OffsetDateTime};

let session = self.session_method.as_ref();

Expand All @@ -572,13 +587,32 @@ where
};
let encoded = crate::protocol::core::Base64UrlJson::from_typed(&request)?;

let default_expires;
let expires = match options.expires {
Some(e) => Some(e),
None => {
let expiry_time = OffsetDateTime::now_utc()
+ Duration::minutes(
crate::protocol::methods::tempo::DEFAULT_EXPIRES_MINUTES as i64,
);
default_expires = expiry_time
.format(&time::format_description::well_known::Rfc3339)
.map_err(|e| {
crate::error::MppError::InvalidConfig(format!(
"failed to format expires: {e}"
))
})?;
Some(default_expires.as_str())
}
};

let id = crate::protocol::methods::tempo::generate_challenge_id(
&self.secret_key,
&self.realm,
"tempo",
"session",
encoded.raw(),
options.expires,
expires,
None,
None,
);
Expand All @@ -589,7 +623,7 @@ where
method: "tempo".into(),
intent: "session".into(),
request: encoded,
expires: options.expires.map(|s| s.to_string()),
expires: expires.map(|s| s.to_string()),
description: options.description.map(|s| s.to_string()),
digest: None,
opaque: None,
Expand Down Expand Up @@ -937,6 +971,9 @@ mod tests {

fn test_credential(secret_key: &str) -> PaymentCredential {
let request = "eyJ0ZXN0IjoidmFsdWUifQ";
let expires = (time::OffsetDateTime::now_utc() + time::Duration::minutes(5))
.format(&time::format_description::well_known::Rfc3339)
.unwrap();
let id = {
#[cfg(feature = "tempo")]
{
Expand All @@ -946,7 +983,7 @@ mod tests {
"mock",
"charge",
request,
None,
Some(&expires),
None,
None,
)
Expand All @@ -963,7 +1000,7 @@ mod tests {
method: "mock".into(),
intent: "charge".into(),
request: crate::protocol::core::Base64UrlJson::from_raw(request),
expires: None,
expires: Some(expires),
digest: None,
opaque: None,
};
Expand Down Expand Up @@ -1174,6 +1211,9 @@ mod tests {
let raw = encoded.raw().to_string();

let secret = "test-secret";
let expires = (time::OffsetDateTime::now_utc() + time::Duration::minutes(5))
.format(&time::format_description::well_known::Rfc3339)
.unwrap();
let id = {
#[cfg(feature = "tempo")]
{
Expand All @@ -1183,7 +1223,7 @@ mod tests {
"mock",
"charge",
&raw,
None,
Some(&expires),
None,
None,
)
Expand All @@ -1200,7 +1240,7 @@ mod tests {
method: "mock".into(),
intent: "charge".into(),
request: crate::protocol::core::Base64UrlJson::from_raw(raw),
expires: None,
expires: Some(expires),
digest: None,
opaque: None,
};
Expand Down Expand Up @@ -1525,6 +1565,10 @@ mod tests {
assert_eq!(challenge.method.as_str(), "tempo");
assert_eq!(challenge.intent.as_str(), "session");
assert!(!challenge.id.is_empty());
assert!(
challenge.expires.is_some(),
"session challenge should have default expires"
);
}

#[cfg(feature = "tempo")]
Expand Down Expand Up @@ -1819,6 +1863,53 @@ mod tests {
);
}

#[cfg(feature = "tempo")]
#[tokio::test]
async fn test_missing_expires_rejected() {
let mpp = create_hmac_test_mpp();

// Manually create a credential without expires — HMAC computed without expires
let request = ChargeRequest {
amount: "100000".into(),
currency: "0x20c0000000000000000000000000000000000000".into(),
recipient: Some("0x742d35Cc6634C0532925a3b844Bc9e7595f1B0F2".into()),
..Default::default()
};
let encoded = crate::protocol::core::Base64UrlJson::from_typed(&request).unwrap();
let id = crate::protocol::methods::tempo::generate_challenge_id(
"test-secret",
"MPP Payment",
"tempo",
"charge",
encoded.raw(),
None,
None,
None,
);

let echo = ChallengeEcho {
id,
realm: "MPP Payment".into(),
method: "tempo".into(),
intent: "charge".into(),
request: encoded,
expires: None,
digest: None,
opaque: None,
};
let credential = PaymentCredential::new(echo, PaymentPayload::hash("0xdeadbeef"));

let result = mpp.verify_credential(&credential).await;
assert!(result.is_err());
let err = result.unwrap_err();
assert_eq!(err.code, Some(ErrorCode::CredentialMismatch));
assert!(
err.message.contains("missing required expires"),
"expected missing expires error, got: {}",
err.message
);
}

#[cfg(feature = "tempo")]
#[tokio::test]
async fn test_verify_credential_with_wrong_amount_rejected() {
Expand Down Expand Up @@ -2023,6 +2114,114 @@ mod tests {
assert_eq!(err.code, Some(ErrorCode::Expired));
}

#[cfg(feature = "tempo")]
#[tokio::test]
async fn test_session_missing_expires_rejected() {
let mpp = create_session_test_mpp();

let request = crate::protocol::intents::SessionRequest {
amount: "1000".into(),
currency: "0x20c0000000000000000000000000000000000000".into(),
recipient: Some("0x742d35Cc6634C0532925a3b844Bc9e7595f1B0F2".into()),
..Default::default()
};
let encoded = crate::protocol::core::Base64UrlJson::from_typed(&request).unwrap();
let id = crate::protocol::methods::tempo::generate_challenge_id(
"test-secret",
"MPP Payment",
"tempo",
"session",
encoded.raw(),
None,
None,
None,
);

let echo = ChallengeEcho {
id,
realm: "MPP Payment".into(),
method: "tempo".into(),
intent: "session".into(),
request: encoded,
expires: None,
digest: None,
opaque: None,
};
let credential = PaymentCredential::new(
echo,
serde_json::json!({
"action": "voucher",
"channelId": "0xabc",
"cumulativeAmount": "5000",
"signature": "0xdef"
}),
);

let result = mpp.verify_session(&credential).await;
assert!(result.is_err());
let err = result.unwrap_err();
assert_eq!(err.code, Some(ErrorCode::CredentialMismatch));
assert!(
err.message.contains("missing required expires"),
"expected missing expires error, got: {}",
err.message
);
}

#[cfg(feature = "tempo")]
#[tokio::test]
async fn test_session_default_expires_accepted() {
let mpp = create_session_test_mpp();

let challenge = mpp
.session_challenge(
"1000",
"0x20c0000000000000000000000000000000000000",
"0x742d35Cc6634C0532925a3b844Bc9e7595f1B0F2",
)
.unwrap();
assert!(
challenge.expires.is_some(),
"session_challenge should set default expires"
);

let echo = challenge.to_echo();
let credential = PaymentCredential::new(
echo,
serde_json::json!({
"action": "voucher",
"channelId": "0xabc",
"cumulativeAmount": "5000",
"signature": "0xdef"
}),
);

let result = mpp.verify_session(&credential).await;
assert!(
result.is_ok(),
"session with default expires should be accepted"
);
}

#[cfg(feature = "tempo")]
#[test]
fn test_session_challenge_with_details_default_expires() {
let mpp = create_session_test_mpp();

let challenge = mpp
.session_challenge_with_details(
"1000",
"0x20c0000000000000000000000000000000000000",
"0x742d35Cc6634C0532925a3b844Bc9e7595f1B0F2",
Default::default(),
)
.unwrap();
assert!(
challenge.expires.is_some(),
"session_challenge_with_details with default options should set default expires"
);
}

// ==================== Stripe tests ====================

#[cfg(feature = "stripe")]
Expand Down
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