[csharp] Fix HTTP signature auth failure on .NET 8 when query params contain special characters

[sagadira]

Summary

Replace compile-time Mustache {{#net90OrLater}} conditional with runtime .NET version detection for URL-encoding query parameter keys in HTTP signature computation.

Problem

When targeting net8.0, the {{#net90OrLater}} Mustache conditional evaluates to false, causing HttpUtility.UrlEncode() to be completely omitted from the generated HttpSigningConfiguration.cs. The generated code becomes:

string key = framework.StartsWith(".NET 9") ? parameter.Key : parameter.Key; // no-op!

Meanwhile, RestSharp 112+ always URL-encodes query parameters on the wire. This mismatch means the HTTP signature is computed over unencoded keys (e.g. $filter) while the actual request sends encoded keys (e.g. %24filter), resulting in HTTP 401 on every request with special characters in query parameter names (OData $filter, $top, $orderby, etc.).

Solution:

Use RuntimeInformation.FrameworkDescription to detect the .NET major version at runtime:

.NET 9+: Skip explicit URL-encoding (HttpUtility.ParseQueryString already encodes keys internally on .NET 9+, so encoding again would cause double-encoding)
.NET 8 and earlier: Explicitly call HttpUtility.UrlEncode(parameter.Key) so the signature matches what RestSharp sends

string framework = RuntimeInformation.FrameworkDescription;
bool skipUrlEncode = framework.StartsWith(".NET ") &&
    int.TryParse(framework.Substring(5).Split('.')[0], out int fwMajor) && fwMajor >= 9;
// ...
string key = skipUrlEncode ? parameter.Key : HttpUtility.UrlEncode(parameter.Key);

PR checklist
Read the contribution guidelines.
Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
Run the following to build the project and update samples:

./mvnw clean package -DskipTests
./bin/generate-samples.sh bin/configs/csharp-restsharp*.yaml bin/configs/csharp-httpclient*.yaml
./bin/utils/export_docs_generators.sh

File the PR against the correct branch: master
If your PR is targeting a particular programming language, @mention the technical committee members for that language.
@muttleyxd @devhl-labs @lucasheim @shibayan (C# generators)

---

Summary by cubic

Fixes HTTP signature auth failures on .NET 8 and ensures correct behavior on .NET 9+ when query parameter names contain special characters by aligning URL-encoding with the actual request. We now detect the .NET version at runtime to decide whether to URL-encode query keys.

• Bug Fixes
  • Replaced Mustache {{#net90OrLater}} with runtime detection via RuntimeInformation.FrameworkDescription.
  • .NET 9+: skip UrlEncode to avoid double-encoding; .NET 8 and earlier: UrlEncode keys to match RestSharp 112+ requests.
  • Updated HttpSigningConfiguration template and regenerated C# samples (httpclient, restsharp, unityWebRequest).

^{Written for commit b56455a. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 12 files

[wing328]

thanks for the PR

cc @mandrean (2017/08) @shibayan (2020/02) @Blackclaws (2021/03) @lucamazzanti (2021/05) @iBicha (2023/07)

[wing328]

what about declaring this boolean flag similar to SigningAlgorithm (a property of this class) and initialize it in the constructor to avoid computing the value every time this function is called?

[sagadira]

refactored skipUrlEncode from a local variable in GetHttpSignedHeader to a private readonly bool _skipUrlEncode field initialized once in the constructor. This avoids recomputing the runtime version check on every call.