fix(storage-blob): normalize backslash to forward slash in SAS canonical resource

[Wu Shuwen (dajiaohuang)]

Fix #48690 - generate_blob_sas backslash normalization

Description

When building the SAS string-to-sign, the SDK was inserting the blob name verbatim into the canonical resource without normalizing backslash () to forward slash (/).

Azure Storage service normalizes \ to / when validating SAS signatures, causing generated SAS tokens to be rejected (HTTP 403) for blob names containing backslashes.

This fix aligns Python SDK behavior with Go and .NET SDKs which already perform this normalization.

Fix

Added path = path.replace("\\", "/") in add_resource_signature() method before building the canonical resource string.

Testing

The issue reporter verified this fix against Azurite (the official Storage emulator).

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[github-actions]

Thank you for your contribution Wu Shuwen (@dajiaohuang)! We will review the pull request and get back to you soon.

[Copilot]

🟡 Changes recommended

An automated regression test for backslash normalization is still needed.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Fixes SAS authentication for blob names containing backslashes by matching Azure Storage canonicalization behavior.

Changes:

• Normalizes backslashes to forward slashes before signing blob resource paths.

File summaries

File	Description
sdk/storage/azure-storage-blob/azure/storage/blob/_shared_access_signature.py	Normalizes the SAS canonical resource path before signature generation.

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 1
• Review effort level: Balanced

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[Wu Shuwen (dajiaohuang)]

Added commit d42de0c with a focused regression test for blob_name="dir\file". It captures the string-to-sign via sts_hook and asserts the canonical resource uses /blob/account/container/dir/file. git diff --check passes. The package test runner is currently blocked in this environment because azure.core and devtools_testutils are not installed; CI should run the new test.

[Copilot]

🟡 Changes recommended

Add the required test-file license header before approval.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

Suppressed comments (1)

sdk/storage/azure-storage-blob/azure/storage/blob/_shared_access_signature.py:356

• This user-visible SAS behavior change is missing from the package's unreleased release notes. Please add an entry under CHANGELOG.md:8 (12.32.0b1 → Bugs Fixed) so customers can discover that backslash-containing blob names now generate valid SAS tokens.

        # Normalize backslashes to forward slashes to match Azure Storage service behavior
        # Go and .NET SDKs already perform this normalization
        path = path.replace("\\", "/")

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Balanced

[Wu Shuwen (dajiaohuang)]

Dependency and runtime follow-up: I installed the existing package development dependencies in an isolated environment (D:\repo\repostew.venv-azure-48849) and ran the focused test from the package directory. python -m pytest tests/test_shared_access_signature.py -q now passes: 1 passed (one unrelated datetime deprecation warning, 24.67s). This confirms the new backslash canonical-resource SAS regression test executes successfully.