feat: Public OAuth uptake for C# libraries (#762)

* Public OAuth uptake for C# libraries

src/Twilio/Annotations/Deprecated.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace Twilio.Annotations
+{
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
+    public class Deprecated : Attribute
+    {
+        public string Message { get; }
+
+        public Deprecated(string message = "This feature is deprecated")
+        {
+            Message = message;
+        }
+    }
+}

src/Twilio/AuthStrategies/AuthStrategy.cs

@@ -0,0 +1,11 @@
+namespace Twilio.AuthStrategies
+{
+    public abstract class AuthStrategy
+    {
+        protected AuthStrategy(){}
+
+        public abstract string GetAuthString();
+
+        public abstract bool RequiresAuthentication();
+    }
+}

src/Twilio/AuthStrategies/Base64UrlEncode.cs

@@ -0,0 +1,32 @@
+#if NET35
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Web.Script.Serialization;
+using Twilio.Annotations;
+
+namespace Twilio.AuthStrategies{
+
+    [Beta]
+    public abstract class Base64UrlEncode
+    {
+        public static string Decode(string base64Url)
+        {
+            // Replace URL-safe characters with Base64 characters
+            string base64 = base64Url
+                .Replace('-', '+')
+                .Replace('_', '/');
+
+            // Add padding if necessary
+            switch (base64.Length % 4)
+            {
+                case 2: base64 += "=="; break;
+                case 3: base64 += "="; break;
+            }
+
+            byte[] bytes = Convert.FromBase64String(base64);
+            return Encoding.UTF8.GetString(bytes);
+        }
+    }
+}
+#endif

src/Twilio/AuthStrategies/BasicAuthStrategy.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Text;
+
+namespace Twilio.AuthStrategies
+{
+    public class BasicAuthStrategy : AuthStrategy
+    {
+        private string username;
+        private string password;
+
+        public BasicAuthStrategy(string username, string password)
+        {
+            this.username = username;
+            this.password = password;
+        }
+
+        public override string GetAuthString()
+        {
+            var credentials = username + ":" + password;
+            var encoded = System.Text.Encoding.UTF8.GetBytes(credentials);
+            var finalEncoded = Convert.ToBase64String(encoded);
+            return $"Basic {finalEncoded}";
+        }
+
+        public override bool RequiresAuthentication()
+        {
+            return true;
+        }
+
+        public override bool Equals(object obj)
+        {
+            if (ReferenceEquals(this, obj)) return true;
+            if (obj == null || GetType() != obj.GetType()) return false;
+            var that = (BasicAuthStrategy)obj;
+            return username == that.username && password == that.password;
+        }
+
+        public override int GetHashCode()
+        {
+            int hash = 17;
+           hash = hash * 31 + (username != null ? username.GetHashCode() : 0);
+           hash = hash * 31 + (password != null ? password.GetHashCode() : 0);
+           return hash;
+        }
+
+    }
+}

src/Twilio/AuthStrategies/NoAuthStrategy.cs

@@ -0,0 +1,17 @@
+namespace Twilio.AuthStrategies
+{
+    public class NoAuthStrategy : AuthStrategy
+    {
+        public NoAuthStrategy(){}
+
+        public override string GetAuthString()
+        {
+            return string.Empty;
+        }
+
+        public override bool RequiresAuthentication()
+        {
+            return false;
+        }
+    }
+}

src/Twilio/AuthStrategies/TokenAuthStrategy.cs

@@ -0,0 +1,155 @@
+using System;
+using System.Threading;
+using Twilio.Http.BearerToken;
+using Twilio.Exceptions;
+
+#if !NET35
+using System.IdentityModel.Tokens.Jwt;
+using System.Threading.Tasks;
+#endif
+
+#if NET35
+using Twilio.Http.Net35;
+using System.Collections.Generic;
+using System.Text;
+using System.Web.Script.Serialization;
+#endif
+
+namespace Twilio.AuthStrategies
+{
+    public class TokenAuthStrategy : AuthStrategy
+    {
+        private string token;
+        private TokenManager tokenManager;
+
+
+        public TokenAuthStrategy(TokenManager tokenManager)
+        {
+            this.tokenManager = tokenManager ?? throw new ArgumentNullException(nameof(tokenManager));
+        }
+
+        public override string GetAuthString()
+        {
+            FetchToken();
+            return $"Bearer {token}";
+        }
+
+        public override bool RequiresAuthentication()
+        {
+            return true;
+        }
+
+        // Token-specific refresh logic
+        private void FetchToken()
+        {
+            if (string.IsNullOrEmpty(token) || tokenExpired(token))
+            {
+                lock (typeof(TokenAuthStrategy))
+                {
+                    if (string.IsNullOrEmpty(token) || tokenExpired(token))
+                    {
+                        token = tokenManager.fetchAccessToken();
+                    }
+                }
+            }
+        }
+
+        public override bool Equals(object obj)
+        {
+            if (ReferenceEquals(this, obj)) return true;
+            if (obj == null || GetType() != obj.GetType()) return false;
+            var that = (TokenAuthStrategy)obj;
+            return token == that.token && tokenManager.Equals(that.tokenManager);
+        }
+
+        public override int GetHashCode()
+        {
+           int hash = 17;
+           hash = hash * 31 + (token != null ? token.GetHashCode() : 0);
+           hash = hash * 31 + (tokenManager != null ? tokenManager.GetHashCode() : 0);
+           return hash;
+        }
+
+
+        public bool tokenExpired(String accessToken){
+            #if NET35
+            return IsTokenExpired(accessToken);
+            #else
+            return isTokenExpired(accessToken);
+            #endif
+        }
+
+#if NET35
+    public static bool IsTokenExpired(string token)
+        {
+            try
+            {
+                // Split the token into its components
+                var parts = token.Split('.');
+                if (parts.Length != 3)
+                    throw new ArgumentException("Malformed token received");
+
+                // Decode the payload (the second part of the JWT)
+                string payload = Base64UrlEncode.Decode(parts[1]);
+
+                // Parse the payload JSON
+                var serializer = new JavaScriptSerializer();
+                var payloadData = serializer.Deserialize<Dictionary<string, object>>(payload);
+
+                // Check the 'exp' claim
+                if (payloadData.TryGetValue("exp", out object expObj))
+                {
+                    if (long.TryParse(expObj.ToString(), out long exp))
+                    {
+                        DateTime expirationDate = UnixTimeStampToDateTime(exp);
+                        return DateTime.UtcNow > expirationDate;
+                    }
+                }
+
+                // If 'exp' claim is missing or not a valid timestamp, consider the token expired
+                throw new ApiConnectionException("token expired");
+                return true;
+            }
+            catch (Exception ex)
+            {
+                // Handle exceptions (e.g., malformed token or invalid JSON)
+                Console.WriteLine($"Error checking token expiration: {ex.Message}");
+                throw new ApiConnectionException("token expired");
+                return true; // Consider as expired if there's an error
+            }
+        }
+
+        private static DateTime UnixTimeStampToDateTime(long unixTimeStamp)
+        {
+            // Unix timestamp is seconds past epoch
+            var epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
+            return epoch.AddSeconds(unixTimeStamp);
+        }
+#endif
+
+#if !NET35
+        public bool isTokenExpired(string token){
+            var handler = new JwtSecurityTokenHandler();
+            try{
+                var jwtToken = handler.ReadJwtToken(token);
+                var exp = jwtToken.Payload.Exp;
+                if (exp.HasValue)
+                    {
+                        var expirationDate = DateTimeOffset.FromUnixTimeSeconds(exp.Value).UtcDateTime;
+                        return DateTime.UtcNow > expirationDate;
+                    }
+                else
+                {
+                    return true; // Assuming token is expired if exp claim is missing
+                }
+            }
+            catch (Exception ex)
+            {
+                Console.WriteLine($"Error reading token: {ex.Message}");
+
+                return true; // Treat as expired if there is an error
+            }
+        }
+#endif
+    }
+}

src/Twilio/Clients/BearerToken/TwilioOrgsTokenRestClient.cs

@@ -28,7 +28,7 @@ namespace Twilio.Clients.BearerToken
     /// <summary>
     /// Implementation of a TwilioRestClient.
     /// </summary>
-    [Beta]
+    [Deprecated]
     public class TwilioOrgsTokenRestClient
     {
         /// <summary>

src/Twilio/Clients/TwilioRestClient.cs

@@ -3,6 +3,7 @@
 using System.Net;
 using Newtonsoft.Json;
 using Twilio.Exceptions;
+using Twilio.AuthStrategies;
 
 #if !NET35
 using System.Threading.Tasks;
@@ -51,6 +52,7 @@ public class TwilioRestClient : ITwilioRestClient
         public string LogLevel { get; set; } = Environment.GetEnvironmentVariable("TWILIO_LOG_LEVEL");
         private readonly string _username;
         private readonly string _password;
+        private readonly AuthStrategy _authstrategy;
 
         /// <summary>
         /// Constructor for a TwilioRestClient
@@ -68,11 +70,13 @@ public TwilioRestClient(
             string accountSid = null,
             string region = null,
             HttpClient httpClient = null,
-            string edge = null
+            string edge = null,
+            AuthStrategy authstrategy = null
         )
         {
             _username = username;
             _password = password;
+            _authstrategy = authstrategy;
 
             AccountSid = accountSid ?? username;
             HttpClient = httpClient ?? DefaultClient();
@@ -89,7 +93,13 @@ public TwilioRestClient(
         /// <returns>response of the request</returns>
         public Response Request(Request request)
         {
-            request.SetAuth(_username, _password);
+
+            if(_username != null && _password != null){
+                request.SetAuth(_username, _password);
+            }
+            else if(_authstrategy != null){
+                request.SetAuth(_authstrategy);
+            }
 
             if (LogLevel == "debug")
                 LogRequest(request);
@@ -102,7 +112,6 @@ public Response Request(Request request)
 
             if (UserAgentExtensions != null)
                 request.UserAgentExtensions = UserAgentExtensions;
-
             Response response;
             try
             {
@@ -132,7 +141,12 @@ public Response Request(Request request)
         /// <returns>Task that resolves to the response of the request</returns>
         public async Task<Response> RequestAsync(Request request)
         {
-            request.SetAuth(_username, _password);
+            if(_username != null && _password != null){
+                request.SetAuth(_username, _password);
+            }
+            else if(_authstrategy != null){
+                request.SetAuth(_authstrategy);
+            }
 
             if (Region != null)
                 request.Region = Region;