How to do Sales Force Authentication from ASP.Net MVC login form using OAuth or SAML protocol?

See more:

C#

ASP.NET

MVC5

OAuth2

SAML

Hi,
I have the requirement like to do sales force authentication from ASP.Net MVC5 web login form using SAML or OAuth protocol

work flow is like:
1.stored user salesforce credentials in SQL db Login table.

2.In Asp.net MVC Login page(User created):
user will give his salesforce credentials and click on submit button.credentails are cross verified with SQL table values,If he is a valid user,it will redirect to other asp.net web page.

3.In this web page, I will provide sales force icon.now user click on this icon,
then user should be redirected to sales force home page without login again from salesforce official login page.

I done the first thing. but struggling for doing second thing.

can one help me??

thanks in advance.