Another way of doing it:
Took some of what is in this blog (uses zocial icons but I found those to be overkill - see css file and you'll know what I mean): http://www.beabigrockstar.com/pretty-social-login-buttons-for-asp-net-mvc-5/
And did it like this:
Startup.Auth.cs
(no extra nothing, just the standard default stuff from an MVC 5 app)
app.UseFacebookAuthentication(appId: "x", appSecret: "x");
app.UseGoogleAuthentication();
CSS:
.socialLoginButton {
cursor:pointer;color:transparent;border:none;width:94px;height:93px;margin-right:20px;
}
.socialLoginButton.facebook {
background:url(/content/images/gui/loginFacebook.png);
}
.socialLoginButton.google {
background:url(/content/images/gui/loginGoogle.png);
}
View:
<button type="submit" class="externalLoginService socialLoginButton @p.AuthenticationType.ToLower()" id="@p.AuthenticationType" name="provider" value="@p.AuthenticationType" title="Log in with @p.Caption">@p.AuthenticationType</button>
Using classes instead of the not so elegant style attribute in the other solution/answer above.