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Fix SigV4 signature for URIs with literal query parameters #674

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Merged
Alan4506 merged 3 commits into from
Mar 31, 2026
+30 −2
Merged

Fix SigV4 signature for URIs with literal query parameters #674

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f37f836
Fix SigV4 signature for URIs with literal query parameters
Alan4506 Mar 30, 2026
40d2dfc
Add unit tests for _format_canonical_query in SigV4Signer
Alan4506 Mar 30, 2026
92be2d2
Fix check-py issues
Alan4506 Mar 31, 2026
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4 changes: 4 additions & 0 deletions ...igners/.changes/next-release/aws-sdk-signers-bugfix-23a4eca5165f48efb1524b95f8498299.json
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
{
"type": "bugfix",
"description": "Fixed SigV4 signature computation for URIs with literal query parameters (e.g., ?sync). parse_qsl was silently dropping query keys without values, causing InvalidSignatureException."
}
4 changes: 2 additions & 2 deletions packages/aws-sdk-signers/src/aws_sdk_signers/signers.py
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Original file line number Diff line number Diff line change
Expand Up @@ -315,7 +315,7 @@ def _format_canonical_query(self, *, query: str | None) -> str:
if query is None:
return ""

query_params = parse_qsl(qs=query)
query_params = parse_qsl(qs=query, keep_blank_values=True)
query_parts = (
(quote(string=key, safe=""), quote(string=value, safe=""))
for key, value in query_params
Expand Down Expand Up @@ -695,7 +695,7 @@ async def _format_canonical_query(self, *, query: str | None) -> str:
if query is None:
return ""

query_params = parse_qsl(qs=query)
query_params = parse_qsl(qs=query, keep_blank_values=True)
query_parts = (
(quote(string=key, safe=""), quote(string=value, safe=""))
for key, value in query_params
Expand Down
24 changes: 24 additions & 0 deletions packages/aws-sdk-signers/tests/unit/test_signers.py
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Expand Up @@ -125,6 +125,18 @@ def test_sign_with_expired_identity(
identity=identity,
)

def test_format_canonical_query_keeps_blank_values(self) -> None:
canonical_query = self.SIGV4_SYNC_SIGNER._format_canonical_query( # pyright: ignore[reportPrivateUsage]
query="foo=bar&baz="
)
assert canonical_query == "baz=&foo=bar"

def test_format_canonical_query_with_literal_query_param(self) -> None:
canonical_query = self.SIGV4_SYNC_SIGNER._format_canonical_query( # pyright: ignore[reportPrivateUsage]
query="sync"
)
assert canonical_query == "sync="


class UnreadableAsyncStream:
def __aiter__(self) -> typing.Self:
Expand Down Expand Up @@ -231,3 +243,15 @@ async def test_sign_event_stream(
assert "X-Amz-Content-SHA256" in signed.fields
payload_hash = signed.fields["X-Amz-Content-SHA256"].as_string()
assert payload_hash == "STREAMING-AWS4-HMAC-SHA256-EVENTS"

async def test_format_canonical_query_keeps_blank_values(self) -> None:
canonical_query = await self.SIGV4_ASYNC_SIGNER._format_canonical_query( # pyright: ignore[reportPrivateUsage]
query="foo=bar&baz="
)
assert canonical_query == "baz=&foo=bar"

async def test_format_canonical_query_with_literal_query_param(self) -> None:
canonical_query = await self.SIGV4_ASYNC_SIGNER._format_canonical_query( # pyright: ignore[reportPrivateUsage]
query="sync"
)
assert canonical_query == "sync="
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