appendix: add OSSA-2026-001 security advisory

[berendt]

Add documentation for CVE-2026-22797, a privilege escalation vulnerability in OpenStack keystonemiddleware's external OAuth2 token handling. Includes OSISM-specific guidance for checking affected configurations and remediation options.

AI-assisted: Claude Code

[github-actions]

✅MegaLinter analysis: Success

Descriptor	Linter	Files	Fixed	Errors	Warnings	Elapsed time
✅ ACTION	actionlint	3		0	0	0.03s
✅ JSON	jsonlint	4		0	0	0.12s
✅ JSON	prettier	4		0	0	0.34s
✅ JSON	v8r	4		0	0	8.04s
✅ MARKDOWN	markdownlint	159		0	0	1.94s
✅ MARKDOWN	markdown-table-formatter	159		0	0	0.3s
✅ REPOSITORY	checkov	yes		no	no	17.07s
✅ REPOSITORY	git_diff	yes		no	no	0.06s
✅ REPOSITORY	secretlint	yes		no	no	1.79s
✅ REPOSITORY	trufflehog	yes		no	no	4.28s
✅ SPELL	cspell	189		0	0	5.07s
✅ SPELL	lychee	176		0	0	6.49s
✅ YAML	prettier	5		0	0	0.39s
✅ YAML	v8r	5		0	0	6.2s
✅ YAML	yamllint	5		0	0	0.37s

See detailed reports in MegaLinter artifacts

Your project could benefit from a custom flavor, which would allow you to run only the linters you need, and thus improve runtime performances. (Skip this info by defining FLAVOR_SUGGESTIONS: false)

• Documentation: Custom Flavors
• Command: npx mega-linter-runner@9.3.0 --custom-flavor-setup --custom-flavor-linters ACTION_ACTIONLINT,JSON_JSONLINT,JSON_V8R,JSON_PRETTIER,MARKDOWN_MARKDOWNLINT,MARKDOWN_MARKDOWN_TABLE_FORMATTER,REPOSITORY_CHECKOV,REPOSITORY_GIT_DIFF,REPOSITORY_SECRETLINT,REPOSITORY_TRUFFLEHOG,SPELL_CSPELL,SPELL_LYCHEE,YAML_PRETTIER,YAML_YAMLLINT,YAML_V8R