[20.09] oauth2_proxy: add patch for CVE-2021-21291

[risicle]

Motivation for this change

https://nvd.nist.gov/vuln/detail/CVE-2021-21291

The function in patched hasn't been touched in 13 months previous to the patch, other than being relocated in the same file. The interface around it looks to be the same judging by its tests. OAuthProxy.whitelistDomains is still an array of strings in the same format. And sure enough the patch applies without a hitch and the added test passes.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[r-rmcgibbo]

Result of nixpkgs-review pr 119899 at d266f7e run on x86_64-linux 1

1 package built successfully:

• oauth2_proxy

1 suggestion:

• warning: missing-patch-comment

  Please add a comment on the line above, explaining the purpose of this patch.
  Near pkgs/servers/oauth2_proxy/default.nix:15:5:

     |
  15 |     (fetchpatch {
     |     ^
  

---

Result of nixpkgs-review pr 119899 at d266f7e run on aarch64-linux 1

1 package built successfully:

• oauth2_proxy

1 suggestion:

• warning: missing-patch-comment

  Please add a comment on the line above, explaining the purpose of this patch.
  Near pkgs/servers/oauth2_proxy/default.nix:15:5:

     |
  15 |     (fetchpatch {
     |     ^