RestSharp.TwitterClient.cs

using System.Text.Json.Serialization;
using RestSharp.Authenticators;

namespace RestSharp.Tests.External.Twitter;

public interface ITwitterClient
{
    Task<TwitterUser> GetUser(string user);
}

public class TwitterClient : ITwitterClient, IDisposable
{
    readonly RestClient _client;

    public TwitterClient(string apiKey, string apiKeySecret)
    {
        var options = new RestClientOptions("https://api.twitter.com/2");

        _client = new RestClient(options)
        {
            Authenticator = new TwitterAuthenticator("https://api.twitter.com", apiKey, apiKeySecret)
        };
    }

    public async Task<TwitterUser> GetUser(string user)
    {
        var response = await _client.GetJsonAsync<TwitterSingleObject<TwitterUser>>(
            "users/by/username/{user}",
            new { user }
        );
        return response!.Data;
    }

    record TwitterSingleObject<T>(T Data);

    public void Dispose()
    {
        _client?.Dispose();
        GC.SuppressFinalize(this);
    }
}

public class TwitterAuthenticator : AuthenticatorBase
{
    readonly string _baseUrl;
    readonly string _clientId;
    readonly string _clientSecret;

    protected DateTime Expiration { get; private set; } = DateTime.MinValue;

    public TwitterAuthenticator(string baseUrl, string clientId, string clientSecret) : base("")
    {
        _baseUrl = baseUrl;
        _clientId = clientId;
        _clientSecret = clientSecret;
    }

    protected override async ValueTask<Parameter> GetAuthenticationParameter(string accessToken)
    {
        if (string.IsNullOrEmpty(Token) || DateTime.UtcNow >= Expiration)
        {
            var tokenResponse = await GetToken();            
            Token = $"{tokenResponse!.TokenType} {tokenResponse!.AccessToken}";
            Expiration = tokenResponse.GetExpirationDate(DateTime.UtcNow);
        }

        return new HeaderParameter(KnownHeaders.Authorization, Token);
    }

    async Task<TokenResponse> GetToken()
    {
        var options = new RestClientOptions(_baseUrl);

        using var client = new RestClient(options)
        {
            Authenticator = new HttpBasicAuthenticator(_clientId, _clientSecret),
        };

        var request = new RestRequest("oauth2/token")
            .AddParameter("grant_type", "client_credentials");

        return await client.PostAsync<TokenResponse>(request);        
    }

    record TokenResponse
    {
        [JsonPropertyName("token_type")]
        public string TokenType { get; init; }
        [JsonPropertyName("access_token")]
        public string AccessToken { get; init; }
        [JsonPropertyName("expires_in")]
        public int ExpiresIn { get; init; }
        
        public DateTime GetExpirationDate(DateTime baseDateTime, int toleranceInMinutes = 1)
        {
            return baseDateTime.AddSeconds(ExpiresIn).AddMinutes(-toleranceInMinutes);
        }
    }
}

public record TwitterUser(string Id, string Name, string Username);