fix(bedrock): sign rerank requests with the shared, header-filtered SigV4 helper

BedrockRerankHandler._prepare_request duplicated ad-hoc SigV4 signing
instead of using BaseAWSLLM.get_request_headers, the helper every other
Bedrock handler (embeddings, converse, invoke, image) already uses.
The duplicate skipped header filtering before signing, so any forwarded
header (e.g. x-forwarded-for) got included in the signed set and could
invalidate the signature if rewritten downstream between signing and
delivery, the same class of bug fixed for the invoke path in #19111.

litellm/llms/bedrock/rerank/handler.py

@@ -135,11 +135,6 @@ class BedrockRerankHandler(BaseAWSLLM):
         data: dict,
         optional_params: dict,
     ) -> BedrockPreparedRequest:
-        try:
-            from botocore.auth import SigV4Auth
-            from botocore.awsrequest import AWSRequest
-        except ImportError:
-            raise ImportError("Missing boto3 to call bedrock. Run 'pip install boto3'.")
         boto3_credentials_info: Final = self._get_boto_credentials_from_optional_params(optional_params, model)
 
         ### SET RUNTIME ENDPOINT ###
@@ -150,24 +145,20 @@ class BedrockRerankHandler(BaseAWSLLM):
         )
         proxy_endpoint_url = proxy_endpoint_url.replace("bedrock-runtime", "bedrock-agent-runtime")
         proxy_endpoint_url = f"{proxy_endpoint_url}/rerank"
-        sigv4: Final = SigV4Auth(
-            boto3_credentials_info.credentials,
-            "bedrock",
-            boto3_credentials_info.aws_region_name,
-        )
-        # Make POST Request
-        body: Final = json.dumps(data).encode("utf-8")
 
+        body: Final = json.dumps(data).encode("utf-8")
         headers = {"Content-Type": "application/json"}
         if extra_headers is not None:
             headers = {"Content-Type": "application/json", **extra_headers}
-        request: Final = AWSRequest(method="POST", url=proxy_endpoint_url, data=body, headers=headers)
-        sigv4.add_auth(request)
-        if (
-            extra_headers is not None and "Authorization" in extra_headers
-        ):  # prevent sigv4 from overwriting the auth header
-            request.headers["Authorization"] = extra_headers["Authorization"]
-        prepped: Final = request.prepare()
+
+        prepped: Final = self.get_request_headers(
+            credentials=boto3_credentials_info.credentials,
+            aws_region_name=boto3_credentials_info.aws_region_name,
+            extra_headers=extra_headers,
+            endpoint_url=proxy_endpoint_url,
+            data=body,
+            headers=headers,
+        )
 
         return BedrockPreparedRequest(
             endpoint_url=proxy_endpoint_url,

tests/test_litellm/llms/bedrock/rerank/test_bedrock_rerank_header_forwarding.py

@@ -17,6 +17,7 @@ sys.path.insert(
 )  # Adds the parent directory to the system path
 import litellm
 from litellm.llms.bedrock.base_aws_llm import Boto3CredentialsInfo
+from litellm.llms.bedrock.rerank.handler import BedrockRerankHandler
 from litellm.llms.custom_httpx.http_handler import AsyncHTTPHandler, HTTPHandler
 
 # Mock response for Bedrock rerank
@@ -408,3 +409,41 @@ def test_bedrock_rerank_extra_headers_and_headers_merge():
 
         except Exception as e:
             pytest.fail(f"Failed to merge and forward headers: {str(e)}")
+
+
+def test_bedrock_rerank_forwarded_headers_excluded_from_sigv4_signature():
+    """
+    A forwarded header like x-forwarded-for can be rewritten between LiteLLM
+    signing the request and AWS receiving it (e.g. by an intermediate load
+    balancer), which invalidates the signature if that header was part of
+    the signed set. It must still reach Bedrock, just unsigned.
+    """
+    from botocore.credentials import Credentials
+
+    handler = BedrockRerankHandler()
+    mock_credentials_info = Boto3CredentialsInfo(
+        credentials=Credentials("test-access-key", "test-secret-key", "test-token"),
+        aws_region_name="us-east-1",
+        aws_bedrock_runtime_endpoint=None,
+    )
+
+    with patch.object(
+        BedrockRerankHandler,
+        "_get_boto_credentials_from_optional_params",
+        return_value=mock_credentials_info,
+    ):
+        prepared_request = handler._prepare_request(
+            model="cohere.rerank-v3-5:0",
+            api_base=None,
+            extra_headers={"x-forwarded-for": "203.0.113.5"},
+            data={"query": test_query, "documents": test_documents},
+            optional_params={},
+        )
+
+    headers = prepared_request["prepped"].headers
+    signed_headers = headers["Authorization"].split("SignedHeaders=")[1].split(",")[0].split(";")
+
+    assert "x-forwarded-for" not in signed_headers, (
+        f"x-forwarded-for must not be part of the SigV4 signature, got SignedHeaders={signed_headers}"
+    )
+    assert headers["x-forwarded-for"] == "203.0.113.5", "forwarded header must still reach Bedrock, unsigned"