chore(waf): fix block_config compatibility (#15208)

Adds a `.get()` method to the `Block_config` class to restore
dictionary-like API compatibility broken by PR #15042, fixing Lambda
integration failures.

PR #15042 changed `Block_config` from a dictionary to a class,
introducing a breaking API change that caused Lambda integration to fail
with:

```
AttributeError: 'Block_config' object has no attribute 'get'
Traceback (most recent call last):
  File "./python/lib/python3.13/site-packages/datadog_lambda/wrapper.py", line 187, in __call__
  File "./python/lib/python3.13/site-packages/datadog_lambda/asm.py", line 220, in get_asm_blocked_response
AttributeError: 'Block_config' object has no attribute 'get'
```

Rollback this ST PR after the merge
DataDog/system-tests@f87f4dd

APPSEC-59959

Author: avara1986

ddtrace/appsec/_utils.py

@@ -173,6 +173,15 @@ def __init__(
         self.location = location.replace(APPSEC.SECURITY_RESPONSE_ID, security_response_id)
         self.content_type: str = "application/json"
 
+    def get(self, method_name: str, default: Any = None) -> Any:
+        """
+        Dictionary-like get method for backward compatibility with Lambda integration.
+
+        Returns the attribute value if it exists, otherwise returns the default value.
+        This allows Block_config to be used in contexts that expect dictionary-like access.
+        """
+        return getattr(self, method_name, default)
+
 
 class Telemetry_result:
     __slots__ = [

tests/appsec/appsec/test_appsec_utils.py

@@ -84,3 +84,114 @@ def test_get_blocked_template_user_file_exists_json():
         assert utils._get_blocked_template("text/html", BLOCK_ID) == utils._format_template(
             BLOCKED_RESPONSE_HTML, BLOCK_ID
         )
+
+
+def test_block_config_get_existing_attribute():
+    """
+    Test that get() returns existing attribute values.
+
+    Regression test for PR #15042 which changed Block_config from dict to class,
+    breaking Lambda integration that expects .get() method for dictionary-like access.
+    """
+    from ddtrace.appsec._utils import Block_config
+
+    config = Block_config(status_code=403, type="auto", grpc_status_code=10)
+
+    assert config.get("status_code") == 403
+    assert config.get("type") == "auto"
+    assert config.get("grpc_status_code") == 10
+
+
+def test_block_config_get_nonexistent_attribute_default_none():
+    """Test that get() returns None for nonexistent attributes when no default is provided."""
+    from ddtrace.appsec._utils import Block_config
+
+    config = Block_config()
+
+    assert config.get("nonexistent_field") is None
+    assert config.get("missing_attribute") is None
+
+
+def test_block_config_get_nonexistent_attribute_with_custom_default():
+    """Test that get() returns custom default for nonexistent attributes."""
+    from ddtrace.appsec._utils import Block_config
+
+    config = Block_config()
+
+    assert config.get("nonexistent_field", "default_value") == "default_value"
+    assert config.get("missing_attribute", 123) == 123
+    assert config.get("another_missing", False) is False
+
+
+def test_block_config_get_all_standard_attributes():
+    """Test that get() works for all standard Block_config attributes."""
+    from ddtrace.appsec._utils import Block_config
+
+    config = Block_config(
+        type="json",
+        status_code=404,
+        grpc_status_code=5,
+        security_response_id="custom-block-id",
+        location="/custom/location",
+    )
+
+    # Test all standard attributes
+    assert config.get("block_id") == "custom-block-id"
+    assert config.get("status_code") == 404
+    assert config.get("grpc_status_code") == 5
+    assert config.get("type") == "json"
+    assert config.get("content_type") == "application/json"
+    # Location should have the security_response_id replaced
+    assert "/custom/location" in config.get("location")
+
+
+def test_block_config_get_method_lambda_compatibility():
+    """
+    Test Lambda integration compatibility scenario.
+
+    This simulates the actual error from Lambda where code expects
+    dictionary-like access: block_config.get("key", default)
+
+    Reproduces the error:
+    AttributeError: 'Block_config' object has no attribute 'get'
+    """
+    from ddtrace.appsec._utils import Block_config
+
+    # Simulate Lambda's get_asm_blocked_response usage
+    block_config = Block_config(
+        type="auto",
+        status_code=403,
+        grpc_status_code=10,
+        security_response_id="block-001",
+    )
+
+    # Lambda code does things like: block_config.get("status_code", 403)
+    status = block_config.get("status_code", 403)
+    assert status == 403
+
+    # Lambda code might check for optional fields
+    custom_field = block_config.get("custom_field", "default")
+    assert custom_field == "default"
+
+    # Verify block_id is accessible
+    block_id = block_config.get("block_id")
+    assert block_id == "block-001"
+
+
+def test_block_config_get_preserves_attribute_access():
+    """Test that adding get() doesn't break normal attribute access."""
+    from ddtrace.appsec._utils import Block_config
+
+    config = Block_config(status_code=500, type="html")
+
+    # Normal attribute access should still work
+    assert config.status_code == 500
+    assert config.type == "html"
+
+    # get() method should return the same values
+    assert config.get("status_code") == 500
+    assert config.get("type") == "html"
+
+    # Both access methods should return identical values
+    assert config.status_code == config.get("status_code")
+    assert config.type == config.get("type")