Validate region string format before use in URL construction#921
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Add _validate_region() that checks region strings against ^[a-z][a-z0-9-]*$ to ensure they match the Azure region naming convention. Validation is applied at discovery time (env var, IMDS) and before URL construction for user-provided azure_region values. Fixes AzureAD#920 Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Pull request overview
This PR adds server-side validation for Azure region strings before they are used to construct regional authority URLs, reducing the risk of malformed authority hosts when region values come from environment variables, IMDS, or user input.
Changes:
- Added
_validate_region()inmsal/region.pyand applied it to region detection paths (env var + IMDS). - Validated
azure_region/configured region values in_get_regional_authority()before constructing regional hosts. - Added
tests/test_region.pyto cover valid/invalid region formats and env var integration.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.
| File | Description |
|---|---|
msal/region.py |
Introduces _validate_region() and applies it to env/IMDS region discovery. |
msal/application.py |
Validates configured region strings before using them to build regional authority hosts. |
tests/test_region.py |
Adds unit tests for region validation and _detect_region() env var behavior. |
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Jun 8, 2026
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Jun 16, 2026
…abel limit Addresses review comment on PR #921: the original regex `^[a-z][a-z0-9-]*$` allowed trailing hyphens (e.g. `eastus-`) and arbitrarily long strings, both of which produce invalid DNS labels in `{region}.login.microsoft.com` URLs. Changed to `^[a-z]([a-z0-9-]{0,61}[a-z0-9])?$` which: - Requires the region to end with an alphanumeric character - Enforces the 63-character DNS label limit Also applied the full set of region-validation changes: - Added `_validate_region()` to msal/region.py - Wired validation into `_detect_region` and `_detect_region_of_azure_vm` - Imported and called `_validate_region` from msal/application.py - Created tests/test_region.py including negative tests for trailing hyphen and overly long strings (> 63 chars)
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Fixes #920
Problem
_detect_region()returns the region string from either theREGION_NAMEenvironment variable or the IMDS endpoint without validating its format. A user-providedazure_regionparameter also flows directly into URL construction. If any of these contain unexpected characters (dots, slashes, etc.), the resulting authority URL could be malformed and lead to misdirected requests.Solution
Added
_validate_region(region, source)inmsal/region.pywhich checks against^[a-z][a-z0-9-]*$(matching the Azure region naming convention, e.g.eastus,westus2,east-us-2). Invalid regions are logged and treated asNone.Validation is applied:
_detect_region()for both the env var and IMDS paths_get_regional_authority()for user-providedazure_regionvaluesTests
Added
tests/test_region.pycovering valid regions, various invalid patterns (dots, slashes, uppercase, leading digits), and env var integration.Reference
RegionManager.ValidateRegion()