Refactor duplicated OAuth2 config and JSON serialization patterns

src/shared/Atlassian.Bitbucket.Tests/BitbucketTokenEndpointResponseJsonTest.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Text.Json;
+using GitCredentialManager;
 using Xunit;
 
 namespace Atlassian.Bitbucket.Tests
@@ -17,11 +18,7 @@ public void BitbucketTokenEndpointResponseJson_Deserialize_Uses_Scopes()
 
             var json = $"{{\"access_token\": \"{accessToken}\", \"token_type\": \"{tokenType}\", \"expires_in\": {expiresIn}, \"scopes\": \"{scopesString}\", \"scope\": \"{scopeString}\"}}";
 
-            var result = JsonSerializer.Deserialize<BitbucketTokenEndpointResponseJson>(json,
-                new JsonSerializerOptions
-                {
-                    PropertyNameCaseInsensitive = true
-                });
+            var result = JsonSerializer.Deserialize<BitbucketTokenEndpointResponseJson>(json, JsonHelper.CaseInsensitiveOptions);
 
             Assert.Equal(accessToken, result.AccessToken);
             Assert.Equal(tokenType, result.TokenType);

src/shared/Atlassian.Bitbucket.Tests/Cloud/UserInfoTest.cs

@@ -3,6 +3,7 @@
 using System.Text.Json.Serialization;
 using System.Threading.Tasks;
 using Atlassian.Bitbucket.Cloud;
+using GitCredentialManager;
 using Xunit;
 
 namespace Atlassian.Bitbucket.Tests.Cloud
@@ -29,10 +30,7 @@ public void Deserialize_UserInfo()
 
             var json = $"{{\"uuid\": \"{uuid}\", \"has_2fa_enabled\": null, \"username\": \"{userName}\", \"account_id\": \"{accountId}\"}}";
 
-            var result = JsonSerializer.Deserialize<UserInfo>(json, new JsonSerializerOptions()
-            {
-                PropertyNameCaseInsensitive = true,
-            });
+            var result = JsonSerializer.Deserialize<UserInfo>(json, JsonHelper.CaseInsensitiveOptions);
 
             Assert.Equal(userName, result.UserName);
         }

src/shared/Atlassian.Bitbucket/Cloud/BitbucketOAuth2Client.cs

@@ -23,44 +23,29 @@ public BitbucketOAuth2Client(HttpClient httpClient, ISettings settings, ITrace2
 
         private static string GetClientId(ISettings settings)
         {
-            // Check for developer override value
-            if (settings.TryGetSetting(
+            return settings.GetOAuthConfigValue(
                 CloudConstants.EnvironmentVariables.OAuthClientId,
-                Constants.GitConfiguration.Credential.SectionName, CloudConstants.GitConfiguration.Credential.OAuthClientId,
-                out string clientId))
-            {
-                return clientId;
-            }
-
-            return CloudConstants.OAuth2ClientId;
+                Constants.GitConfiguration.Credential.SectionName,
+                CloudConstants.GitConfiguration.Credential.OAuthClientId,
+                CloudConstants.OAuth2ClientId);
         }
 
         private static Uri GetRedirectUri(ISettings settings)
         {
-            // Check for developer override value
-            if (settings.TryGetSetting(
+            return settings.GetOAuthConfigUri(
                 CloudConstants.EnvironmentVariables.OAuthRedirectUri,
-                Constants.GitConfiguration.Credential.SectionName, CloudConstants.GitConfiguration.Credential.OAuthRedirectUri,
-                out string redirectUriStr) && Uri.TryCreate(redirectUriStr, UriKind.Absolute, out Uri redirectUri))
-            {
-                return redirectUri;
-            }
-
-            return CloudConstants.OAuth2RedirectUri;
+                Constants.GitConfiguration.Credential.SectionName,
+                CloudConstants.GitConfiguration.Credential.OAuthRedirectUri,
+                CloudConstants.OAuth2RedirectUri);
         }
 
         private static string GetClientSecret(ISettings settings)
         {
-            // Check for developer override value
-            if (settings.TryGetSetting(
+            return settings.GetOAuthConfigValue(
                 CloudConstants.EnvironmentVariables.OAuthClientSecret,
-                Constants.GitConfiguration.Credential.SectionName, CloudConstants.GitConfiguration.Credential.OAuthClientSecret,
-                out string clientSecret))
-            {
-                return clientSecret;
-            }
-
-            return CloudConstants.OAuth2ClientSecret;
+                Constants.GitConfiguration.Credential.SectionName,
+                CloudConstants.GitConfiguration.Credential.OAuthClientSecret,
+                CloudConstants.OAuth2ClientSecret);
         }
 
         private static OAuth2ServerEndpoints GetEndpoints()

src/shared/Atlassian.Bitbucket/Cloud/BitbucketRestApi.cs

@@ -43,11 +43,7 @@ public async Task<RestApiResult<IUserInfo>> GetUserInformationAsync(string userN
 
                     if (response.IsSuccessStatusCode)
                     {
-                        var obj = JsonSerializer.Deserialize<UserInfo>(json,
-                            new JsonSerializerOptions
-                            {
-                                PropertyNameCaseInsensitive = true,
-                            });
+                        var obj = JsonSerializer.Deserialize<UserInfo>(json, JsonHelper.CaseInsensitiveOptions);
 
                         return new RestApiResult<IUserInfo>(response.StatusCode, obj);
                     }

src/shared/Atlassian.Bitbucket/DataCenter/BitbucketOAuth2Client.cs

@@ -26,44 +26,29 @@ public BitbucketOAuth2Client(HttpClient httpClient, ISettings settings, ITrace2
 
         private static string GetClientId(ISettings settings)
         {
-            // Check for developer override value
-            if (settings.TryGetSetting(
+            return settings.GetRequiredOAuthConfigValue(
                 DataCenterConstants.EnvironmentVariables.OAuthClientId,
-                Constants.GitConfiguration.Credential.SectionName, DataCenterConstants.GitConfiguration.Credential.OAuthClientId,
-                out string clientId))
-            {
-                return clientId;
-            }
-
-            throw new ArgumentException("Bitbucket DC OAuth Client ID must be defined");
+                Constants.GitConfiguration.Credential.SectionName,
+                DataCenterConstants.GitConfiguration.Credential.OAuthClientId,
+                "Bitbucket DC OAuth Client ID must be defined");
         }
 
         private static Uri GetRedirectUri(ISettings settings)
         {
-            // Check for developer override value
-            if (settings.TryGetSetting(
+            return settings.GetOAuthConfigUri(
                 DataCenterConstants.EnvironmentVariables.OAuthRedirectUri,
-                Constants.GitConfiguration.Credential.SectionName, DataCenterConstants.GitConfiguration.Credential.OAuthRedirectUri,
-                out string redirectUriStr) && Uri.TryCreate(redirectUriStr, UriKind.Absolute, out Uri redirectUri))
-            {
-                return redirectUri;
-            }
-
-            return DataCenterConstants.OAuth2RedirectUri;
+                Constants.GitConfiguration.Credential.SectionName,
+                DataCenterConstants.GitConfiguration.Credential.OAuthRedirectUri,
+                DataCenterConstants.OAuth2RedirectUri);
         }
 
         private static string GetClientSecret(ISettings settings)
         {
-            // Check for developer override value
-            if (settings.TryGetSetting(
+            return settings.GetRequiredOAuthConfigValue(
                 DataCenterConstants.EnvironmentVariables.OAuthClientSecret,
-                Constants.GitConfiguration.Credential.SectionName, DataCenterConstants.GitConfiguration.Credential.OAuthClientSecret,
-                out string clientSecret))
-            {
-                return clientSecret;
-            }
-
-            throw new ArgumentException("Bitbucket DC OAuth Client Secret must be defined");
+                Constants.GitConfiguration.Credential.SectionName,
+                DataCenterConstants.GitConfiguration.Credential.OAuthClientSecret,
+                "Bitbucket DC OAuth Client Secret must be defined");
         }
 
         private static OAuth2ServerEndpoints GetEndpoints(ISettings settings)

src/shared/Atlassian.Bitbucket/DataCenter/BitbucketRestApi.cs

@@ -107,12 +107,7 @@ public async Task<List<AuthenticationMethod>> GetAuthenticationMethodsAsync()
 
                     if (response.IsSuccessStatusCode)
                     {
-                        var loginOptions = JsonSerializer.Deserialize<LoginOptions>(json,
-                            new JsonSerializerOptions
-                            {
-                                PropertyNameCaseInsensitive = true,
-                                DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
-                            });
+                        var loginOptions = JsonSerializer.Deserialize<LoginOptions>(json, JsonHelper.CaseInsensitiveIgnoreNullOptions);
 
                         if (loginOptions.Results.Any(r => "LOGIN_FORM".Equals(r.Type)))
                         {

src/shared/Core.Tests/TokenEndpointResponseJsonTest.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Text.Json;
+using GitCredentialManager;
 using GitCredentialManager.Authentication.OAuth.Json;
 using Xunit;
 
@@ -17,11 +18,7 @@ public void TokenEndpointResponseJson_Deserialize_Uses_Scope()
         var scopeString = "a,b,c";
         var json = $"{{\"access_token\": \"{accessToken}\", \"token_type\": \"{tokenType}\", \"expires_in\": {expiresIn}, \"scopes\": \"{scopesString}\", \"scope\": \"{scopeString}\"}}";
 
-        var result = JsonSerializer.Deserialize<TokenEndpointResponseJson>(json,
-            new JsonSerializerOptions
-            {
-                PropertyNameCaseInsensitive = true
-            });
+        var result = JsonSerializer.Deserialize<TokenEndpointResponseJson>(json, JsonHelper.CaseInsensitiveOptions);
 
         Assert.Equal(accessToken, result.AccessToken);
         Assert.Equal(tokenType, result.TokenType);

src/shared/Core/Authentication/OAuth/OAuth2Client.cs

@@ -321,10 +321,7 @@ public async Task<OAuth2TokenResult> GetTokenByDeviceCodeAsync(OAuth2DeviceCodeR
                             return result;
                         }
 
-                        var error = JsonSerializer.Deserialize<ErrorResponseJson>(json, new JsonSerializerOptions
-                        {
-                            PropertyNameCaseInsensitive = true
-                        });
+                        var error = JsonSerializer.Deserialize<ErrorResponseJson>(json, JsonHelper.CaseInsensitiveOptions);
 
                         switch (error.Error)
                         {

src/shared/Core/Authentication/OAuth/OAuth2SettingsHelper.cs

@@ -0,0 +1,84 @@
+using System;
+
+namespace GitCredentialManager.Authentication.OAuth
+{
+    /// <summary>
+    /// Helper class for retrieving OAuth2 configuration settings from environment variables or Git configuration.
+    /// </summary>
+    public static class OAuth2SettingsHelper
+    {
+        /// <summary>
+        /// Retrieves an OAuth configuration value from settings, with fallback to a default value.
+        /// </summary>
+        /// <param name="settings">The settings instance to query.</param>
+        /// <param name="environmentVariable">The environment variable name.</param>
+        /// <param name="configSection">The Git configuration section name.</param>
+        /// <param name="configProperty">The Git configuration property name.</param>
+        /// <param name="defaultValue">The default value to return if no setting is found.</param>
+        /// <returns>The configured value if found, otherwise the default value.</returns>
+        public static string GetOAuthConfigValue(
+            this ISettings settings,
+            string environmentVariable,
+            string configSection,
+            string configProperty,
+            string defaultValue)
+        {
+            if (settings.TryGetSetting(environmentVariable, configSection, configProperty, out string value))
+            {
+                return value;
+            }
+
+            return defaultValue;
+        }
+
+        /// <summary>
+        /// Retrieves a required OAuth configuration value from settings, throwing an exception if not found.
+        /// </summary>
+        /// <param name="settings">The settings instance to query.</param>
+        /// <param name="environmentVariable">The environment variable name.</param>
+        /// <param name="configSection">The Git configuration section name.</param>
+        /// <param name="configProperty">The Git configuration property name.</param>
+        /// <param name="errorMessage">The error message to include in the exception if the value is not found.</param>
+        /// <returns>The configured value.</returns>
+        /// <exception cref="ArgumentException">Thrown when the required value is not found.</exception>
+        public static string GetRequiredOAuthConfigValue(
+            this ISettings settings,
+            string environmentVariable,
+            string configSection,
+            string configProperty,
+            string errorMessage)
+        {
+            if (settings.TryGetSetting(environmentVariable, configSection, configProperty, out string value))
+            {
+                return value;
+            }
+
+            throw new ArgumentException(errorMessage);
+        }
+
+        /// <summary>
+        /// Retrieves an OAuth configuration URI from settings, with fallback to a default value.
+        /// </summary>
+        /// <param name="settings">The settings instance to query.</param>
+        /// <param name="environmentVariable">The environment variable name.</param>
+        /// <param name="configSection">The Git configuration section name.</param>
+        /// <param name="configProperty">The Git configuration property name.</param>
+        /// <param name="defaultValue">The default URI to return if no setting is found.</param>
+        /// <returns>The configured URI if found and valid, otherwise the default URI.</returns>
+        public static Uri GetOAuthConfigUri(
+            this ISettings settings,
+            string environmentVariable,
+            string configSection,
+            string configProperty,
+            Uri defaultValue)
+        {
+            if (settings.TryGetSetting(environmentVariable, configSection, configProperty, out string uriStr) &&
+                Uri.TryCreate(uriStr, UriKind.Absolute, out Uri uri))
+            {
+                return uri;
+            }
+
+            return defaultValue;
+        }
+    }
+}

src/shared/Core/JsonHelper.cs

@@ -0,0 +1,35 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace GitCredentialManager
+{
+    /// <summary>
+    /// Helper class providing common JSON serialization options and utilities.
+    /// </summary>
+    /// <remarks>
+    /// The shared JsonSerializerOptions instances should not be modified after initialization
+    /// to ensure thread safety across the application.
+    /// </remarks>
+    public static class JsonHelper
+    {
+        /// <summary>
+        /// Gets JSON serializer options configured for case-insensitive property names.
+        /// Do not modify this instance; create a new instance if different options are needed.
+        /// </summary>
+        public static JsonSerializerOptions CaseInsensitiveOptions { get; } = new JsonSerializerOptions
+        {
+            PropertyNameCaseInsensitive = true
+        };
+
+        /// <summary>
+        /// Gets JSON serializer options configured for case-insensitive property names
+        /// and ignoring null values when writing.
+        /// Do not modify this instance; create a new instance if different options are needed.
+        /// </summary>
+        public static JsonSerializerOptions CaseInsensitiveIgnoreNullOptions { get; } = new JsonSerializerOptions
+        {
+            PropertyNameCaseInsensitive = true,
+            DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
+        };
+    }
+}

src/shared/GitHub/GitHubOAuth2Client.cs

@@ -28,47 +28,34 @@ private static OAuth2ServerEndpoints CreateEndpoints(Uri uri)
 
         private static string GetClientId(ISettings settings)
         {
-            // Check for developer override value
-            if (settings.TryGetSetting(
+            return settings.GetOAuthConfigValue(
                 GitHubConstants.EnvironmentVariables.DevOAuthClientId,
-                Constants.GitConfiguration.Credential.SectionName, GitHubConstants.GitConfiguration.Credential.DevOAuthClientId,
-                out string clientId))
-            {
-                return clientId;
-            }
-
-            return GitHubConstants.OAuthClientId;
+                Constants.GitConfiguration.Credential.SectionName,
+                GitHubConstants.GitConfiguration.Credential.DevOAuthClientId,
+                GitHubConstants.OAuthClientId);
         }
 
         private static Uri GetRedirectUri(ISettings settings, Uri targetUri)
         {
-            // Check for developer override value
-            if (settings.TryGetSetting(
-                GitHubConstants.EnvironmentVariables.DevOAuthRedirectUri,
-                Constants.GitConfiguration.Credential.SectionName, GitHubConstants.GitConfiguration.Credential.DevOAuthRedirectUri,
-                out string redirectUriStr) && Uri.TryCreate(redirectUriStr, UriKind.Absolute, out Uri redirectUri))
-            {
-                return redirectUri;
-            }
-
             // Only GitHub.com supports the new OAuth redirect URI today
-            return GitHubHostProvider.IsGitHubDotCom(targetUri)
+            Uri defaultUri = GitHubHostProvider.IsGitHubDotCom(targetUri)
                 ? GitHubConstants.OAuthRedirectUri
                 : GitHubConstants.OAuthLegacyRedirectUri;
+
+            return settings.GetOAuthConfigUri(
+                GitHubConstants.EnvironmentVariables.DevOAuthRedirectUri,
+                Constants.GitConfiguration.Credential.SectionName,
+                GitHubConstants.GitConfiguration.Credential.DevOAuthRedirectUri,
+                defaultUri);
         }
 
         private static string GetClientSecret(ISettings settings)
         {
-            // Check for developer override value
-            if (settings.TryGetSetting(
+            return settings.GetOAuthConfigValue(
                 GitHubConstants.EnvironmentVariables.DevOAuthClientSecret,
-                Constants.GitConfiguration.Credential.SectionName, GitHubConstants.GitConfiguration.Credential.DevOAuthClientSecret,
-                out string clientSecret))
-            {
-                return clientSecret;
-            }
-
-            return GitHubConstants.OAuthClientSecret;
+                Constants.GitConfiguration.Credential.SectionName,
+                GitHubConstants.GitConfiguration.Credential.DevOAuthClientSecret,
+                GitHubConstants.OAuthClientSecret);
         }
     }
 }