feat: Adding example for using public OAuth (#769)

* Adding example for using public OAuth

Author: AsabuHere

README.md

@@ -72,8 +72,12 @@ var message = MessageResource.Create(
 );
 Console.WriteLine(message.Sid);
 ```
+## OAuth Feature for Twilio APIs
+We are introducing Client Credentials Flow-based OAuth 2.0 authentication. This feature is currently in beta and its implementation is subject to change.
 
-Examples on how to make rest calls with bearer token authentication is added [here](https://github.com/twilio/twilio-csharp/blob/orgs_api_uptake/examples/BearerTokenAuthentication.md)
+API examples [here](https://github.com/twilio/twilio-csharp/blob/main/examples/PublicOAuthAuthentication.md)
+
+Organisation API examples [here](https://github.com/twilio/twilio-csharp/blob/main/examples/BearerTokenAuthentication.md)
 
 ## Specify Region and/or Edge
 

examples/BearerTokenAuthentication.md

@@ -13,7 +13,7 @@ class Program
     static void Main(string[] args)
     {
 
-        CredentialProvider credentialProvider = new ClientCredentialProvider(CLIENT_ID, CLIENT_SECRET);
+        CredentialProvider credentialProvider = new OrgsClientCredentialProvider(CLIENT_ID, CLIENT_SECRET);
         TwilioClient.Init(credentialProvider);
 
         Twilio.Base.ResourceSet<Twilio.Rest.PreviewIam.Organizations.AccountResource> accountList = null;

examples/PublicOAuthAuthentication.md

@@ -0,0 +1,25 @@
+```csharp
+using Twilio;
+using Twilio.Credential;
+using Twilio.Rest.Api.V2010.Account;
+
+//Find client id, client secret of the OAuth App
+//Message sid in this example is the sid of any previously sent message
+class Program
+{
+    static void Main(string[] args)
+    {
+        CredentialProvider credentialProvider = new ClientCredentialProvider(CLIENT_ID, CLIENT_SECRET);
+        TwilioClient.Init(credentialProvider, ACCOUNT_SID);
+
+        /*
+         * Or use the following if accountSid is not required as a path parameter for an API or when setting accountSid in the API.
+           TwilioClient.init(new ClientCredentialProvider(CLIENT_ID, CLIENT_SECRET));
+         */
+        
+        FetchMessageOptions fm = new FetchMessageOptions(MESSAGE_SID);
+        MessageResource m = MessageResource.Fetch(fm);
+        Console.WriteLine(m.Body);
+    }
+}
+```