Refactor duplicated OAuth2 config and JSON serialization patterns

[Copilot]

Problem

Identical TryGetSetting patterns repeated across 4 OAuth2 client implementations. Duplicate JsonSerializerOptions initialization in 6+ files.

Changes

OAuth2 Configuration Utilities

Consolidated duplicated setting retrieval into OAuth2SettingsHelper:

// Before (repeated 4 times across GitHub, GitLab, Bitbucket clients)
if (settings.TryGetSetting(
    Constants.EnvironmentVariables.DevOAuthClientId,
    Constants.GitConfiguration.Credential.SectionName, 
    Constants.GitConfiguration.Credential.DevOAuthClientId,
    out string clientId))
{
    return clientId;
}
return Constants.OAuthClientId;

// After
return settings.GetOAuthConfigValue(
    Constants.EnvironmentVariables.DevOAuthClientId,
    Constants.GitConfiguration.Credential.SectionName,
    Constants.GitConfiguration.Credential.DevOAuthClientId,
    Constants.OAuthClientId);

Methods provided:

• GetOAuthConfigValue() - optional config with fallback
• GetRequiredOAuthConfigValue() - required config, throws if missing
• GetOAuthConfigUri() - URI config with validation

Files refactored:

• GitHub/GitHubOAuth2Client.cs
• GitLab/GitLabOAuth2Client.cs
• Atlassian.Bitbucket/Cloud/BitbucketOAuth2Client.cs
• Atlassian.Bitbucket/DataCenter/BitbucketOAuth2Client.cs

JSON Serialization Options

Created shared JsonHelper with reusable configurations:

// Before (repeated in 6+ files)
JsonSerializer.Deserialize<T>(json, new JsonSerializerOptions
{
    PropertyNameCaseInsensitive = true
});

// After
JsonSerializer.Deserialize<T>(json, JsonHelper.CaseInsensitiveOptions);

Shared instances:

• JsonHelper.CaseInsensitiveOptions
• JsonHelper.CaseInsensitiveIgnoreNullOptions

Files refactored:

• REST API implementations: BitbucketRestApi.cs (Cloud/DataCenter), OAuth2Client.cs
• Test files: BitbucketTokenEndpointResponseJsonTest.cs, UserInfoTest.cs, TokenEndpointResponseJsonTest.cs

Impact

~160 lines of duplication eliminated across 12 files. Thread-safety documented for shared instances.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• av-build-tel-api-v1.avaloniaui.net
  • Triggering command: /usr/share/dotnet/dotnet dotnet exec --runtimeconfig /home/REDACTED/.nuget/packages/avalonia.buildservices/0.0.29/tools/netstandard2.0/runtimeconfig.json /home/REDACTED/.nuget/packages/avalonia.buildservices/0.0.29/tools/netstandard2.0/Avalonia.BuildServices.Collector.dll (dns block)
• www.apple.com
  • Triggering command: /opt/hostedtoolcache/CodeQL/2.24.1/x64/codeql/tools/linux64/java/bin/java /opt/hostedtoolcache/CodeQL/2.24.1/x64/codeql/tools/linux64/java/bin/java -jar /opt/hostedtoolcache/CodeQL/2.24.1/x64/codeql/xml/tools/xml-extractor.jar --fileList=/home/REDACTED/work/git-credential-manager/.codeql-scratch/dbs/csharp/working/files-to-index4456684017528651772.list --sourceArchiveDir=/home/REDACTED/work/git-credential-manager/.codeql-scratch/dbs/csharp/src --outputDir=/home/REDACTED/work/git-credential-manager/.codeql-scratch/dbs/csharp/trap/csharp -manager/git-credential-manager//low:false dll xQ465H/tmp7f58dcgit (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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