Campaign_Tracker/Campaign_Tracker.Server/Authentication/KeycloakTokenClient.cs

using System.Net;
using System.Text.Json.Serialization;
using Microsoft.Extensions.Options;

namespace Campaign_Tracker.Server.Authentication;

public interface IKeycloakTokenClient
{
    Task<AuthTokenSetResponse> ExchangeAuthorizationCodeAsync(
        string code,
        string redirectUri,
        CancellationToken cancellationToken);

    Task<AuthTokenSetResponse> RefreshAccessTokenAsync(
        string refreshToken,
        CancellationToken cancellationToken);
}

public sealed class KeycloakTokenClient : IKeycloakTokenClient
{
    private readonly HttpClient _httpClient;
    private readonly ILogger<KeycloakTokenClient> _logger;
    private readonly KeycloakOptions _options;

    public KeycloakTokenClient(
        HttpClient httpClient,
        IOptions<KeycloakOptions> options,
        ILogger<KeycloakTokenClient> logger)
    {
        _httpClient = httpClient;
        _logger = logger;
        _options = options.Value;
    }

    public Task<AuthTokenSetResponse> ExchangeAuthorizationCodeAsync(
        string code,
        string redirectUri,
        CancellationToken cancellationToken)
    {
        return RequestTokenSetAsync(
            new Dictionary<string, string>
            {
                ["grant_type"] = "authorization_code",
                ["client_id"] = _options.ClientId,
                ["client_secret"] = GetClientSecret(),
                ["redirect_uri"] = redirectUri,
                ["code"] = code,
            },
            cancellationToken);
    }

    public Task<AuthTokenSetResponse> RefreshAccessTokenAsync(
        string refreshToken,
        CancellationToken cancellationToken)
    {
        return RequestTokenSetAsync(
            new Dictionary<string, string>
            {
                ["grant_type"] = "refresh_token",
                ["client_id"] = _options.ClientId,
                ["client_secret"] = GetClientSecret(),
                ["refresh_token"] = refreshToken,
            },
            cancellationToken);
    }

    private async Task<AuthTokenSetResponse> RequestTokenSetAsync(
        Dictionary<string, string> formValues,
        CancellationToken cancellationToken)
    {
        using var content = new FormUrlEncodedContent(formValues);
        using var response = await _httpClient.PostAsync(TokenEndpoint, content, cancellationToken);

        if (!response.IsSuccessStatusCode)
        {
            var errorBody = await response.Content.ReadAsStringAsync(cancellationToken);
            _logger.LogWarning(
                "Keycloak token request failed with {StatusCode}: {ErrorBody}",
                (int)response.StatusCode,
                errorBody);
            throw new KeycloakTokenRequestException(response.StatusCode, errorBody);
        }

        var payload = await response.Content
            .ReadFromJsonAsync<KeycloakTokenResponse>(cancellationToken)
            ?? throw new InvalidOperationException("Keycloak token response was empty.");

        return new AuthTokenSetResponse(
            payload.AccessToken,
            payload.RefreshToken,
            DateTimeOffset.UtcNow.AddSeconds(payload.ExpiresIn).ToUnixTimeSeconds());
    }

    private string TokenEndpoint =>
        $"{_options.TokenEndpointAuthority.TrimEnd('/')}/protocol/openid-connect/token";

    private string GetClientSecret()
    {
        if (string.IsNullOrWhiteSpace(_options.ClientSecret))
        {
            throw new InvalidOperationException("Keycloak client secret is not configured.");
        }

        return _options.ClientSecret;
    }
}

public sealed class KeycloakTokenRequestException : Exception
{
    public KeycloakTokenRequestException(HttpStatusCode statusCode, string responseBody)
        : base($"Keycloak token request failed with status {(int)statusCode}.")
    {
        StatusCode = statusCode;
        ResponseBody = responseBody;
    }

    public HttpStatusCode StatusCode { get; }

    public string ResponseBody { get; }
}

public sealed record AuthTokenSetResponse(
    string AccessToken,
    string RefreshToken,
    long ExpiresAtEpochSeconds);

internal sealed class KeycloakTokenResponse
{
    [JsonPropertyName("access_token")]
    public string AccessToken { get; init; } = string.Empty;

    [JsonPropertyName("refresh_token")]
    public string RefreshToken { get; init; } = string.Empty;

    [JsonPropertyName("expires_in")]
    public int ExpiresIn { get; init; }
}