DEV-15456: Added validation methods for group and filter fields to prevent regex injection

[gregrholden]

Description:

DEV-15456: Sanitize Postgres input [f112]
Fixing a vulnerability that allowed unauthenticated attackers to inject arbitrary Django ORM lookup suffixes (particularly __regex/__iregex) into aggregate group parameters and filter field paths, enabling regex DoS attacks and schema enumeration.
AC: Implement model-based validation that validates field paths against Django model schemas.

Technical Details:

Changes:

• Aggregate Group Validation (common/mixins.py):
  • Added _resolve_field_path() method to validate group parameter fields segment-by-segment.
  • Validates fields against model schema using Django's _meta.get_field() API.
  • Supports legitimate FK traversal (e.g., treasury_account__federal_account_id).
  • Allows safe transform suffixes (e.g., __fy) defined in _sql_function_transformations (line 78).
  • Raises InvalidParameterException for invalid field paths.
  • NOTE: Also needed to update return value definitions across the file, and reorder imports, to pass lint tests.
• Filter Field Validation (common/api_request_utils.py):
  • Added _validate_filter_field() and _resolve_field_path() methods to FilterGenerator.
  • Validates POST filter field parameters before creating Q objects.
  • Validates GET query parameter keys before use in filters.
  • Added _get_allowed_lookups() that derives safe Django lookups from operators dictionary.
  • Explicitly blocks __regex and __iregex lookups to prevent ReDoS attacks.
  • Supports compound lookups (e.g., __len__gt for ArrayField length checks).
  • Handles special cases: field arrays for range_intersect and search operations.

Requirements for PR Merge:

1. Unit & integration tests updated
2. API documentation updated (examples listed below)
   1. API Contracts
   2. API UI
   3. Comments
3. Data validation completed (examples listed below)
   1. Does this work well with the current frontend? Or is the frontend aware of a needed change?
   2. Is performance impacted in the changes (e.g., API, pipeline, downloads, etc.)?
   3. Is the expected data returned with the expected format?
4. Appropriate Operations ticket(s) created
5. Jira Ticket(s)
   1. DEV-0

Explain N/A in above checklist:

[sethstoudenmier]

Overall LGTM! Ideally, we will move away from the v1 endpoints and replace with v2, but this is a great middle ground for now.

[james-at-kc]

Now uses f"" strings throughout per suggestion.

[james-at-kc]

LGTM. improved code by using f-strings as suggested in previous approval.