Navigate to a website and set claims - asp.net

Question

I need to navigate to a web site and set a number of claims for that web site to use, but I cannot find any explanation on how to do it. I must be googling the wrong words.
I'm using c# and .Net framework 4.6.1
Edit 1
I was asked to explain my challenge better. I am developing 2 separate websites. Users will always go to website A where they will authenticated using Azure B2C. Once authenticated they will perform a few actions after which they will be navigated to website B. Azure B2C passes user data to website A using Claims, which I would like to forward to website B

Answer 1

What you need to do is to expose a new login action in your website B. This login action can receive an encrypted token which inside contains the claims you are interested in forwarding to the site B. Once that encrypted token is received, the website B can decrypt it and recreate the claims that you are interested in. You can use the built in JwtSecurityToken Handler:
https://msdn.microsoft.com/en-us/library/system.identitymodel.tokens.jwtsecuritytokenhandler(v=vs.114).aspx
For example:
public string CreateSecurityToken(string audience, IEnumerable<Claim> claims)
{
if (claims == null) return null;
var credentials = new SigningCredentials(
new InMemorySymmetricSecurityKey(Encoding.UTF8.GetBytes("SOMEKEY")),
"http://www.w3.org/2001/04/xmldsig-more#hmac-sha256",
"http://www.w3.org/2001/04/xmlenc#sha256");
var claimsIdentity = new ClaimsIdentity(claims, "Custom Authentication", System.Security.Claims.ClaimTypes.Name, System.Security.Claims.ClaimTypes.Role);
var tokenDescriptor = new SecurityTokenDescriptor
{
Subject = claimsIdentity,
TokenIssuerName = TokenIssuer,
AppliesToAddress = "http://" + audience,
Lifetime = new Lifetime(DateTime.UtcNow, DateTime.UtcNow.AddMinutes(GetTokenExpirationMinutes(audience))),
SigningCredentials = credentials
};
var jwtHandler = new JwtSecurityTokenHandler();
var token = jwtHandler.CreateToken(tokenDescriptor);
return jwtHandler.WriteToken(token);
}
this will create a token which you can send to a login method on website B

Answer 2

A claim from website A will not be sent to website B.
This could work this way:
A users logs on to site A (using credentials from B2C)
User saves info into B2C (using Graph API)
Redirect to Site B
User logs on to site B (this can occur without prompting the user, same B2C)
Claim are created for site B, but they can contain values set during step 2
graph API:
https://azure.microsoft.com/en-us/documentation/articles/active-directory-b2c-devquickstarts-graph-dotnet/
If the info is already in the B2C directory, the example is even more simple, create 2 sites:
https://azure.microsoft.com/nl-nl/documentation/articles/active-directory-b2c-devquickstarts-web-dotnet/
Create a custom attribute to store the information:
https://azure.microsoft.com/nl-nl/documentation/articles/active-directory-b2c-reference-custom-attr/
Create a B2C custom attribute:
Create 2(both) B2C Applications
Create a single B2C sign-in policy using the custom attribute and add it to the claims
Use the same policy in both applications, both should see the same claim