Quote:
1.Is it compulsory to have SSL
Not compulsory, but a very good approach, as the web app of Facebook or Google would know that you the communication is
secure.
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2.Is there any third party pluggin or app for the same above.
Apart from third-party, Google and Facebook both have developer documentations that you can easily read and implement in ASP.NET.
Sad thing about these two giants is, that they do not officially support .NET framework. They support, PHP, Node.js, or simple JavaScript. So, what you would need to do is to implement this feature using JavaScript.
Have a look at the following links,
Google Identity Platform | Google Developers[
^]
Facebook Login API[
^]
Edit
As mentioned in the comments, you can also utilize the OAuth libraries,
OAuth .NET library[
^]. For this, you would also require to know a few endpoints for communication in the server-client environment.