Best practice for saving tokens using client credential stream

Question

I have an ASP.NET Core MVC application that allows anonymous users. This application calls the ASP.NET web API, which is protected by Identity Server 4. I created a client in Identity Server that describes the MVC application (client) and gave it access to the api area as follows:

new Client
{
    ClientId = "my-mvc-client-app",
    AllowedGrantTypes = GrantTypes.ClientCredentials,

    RequireConsent = false,
    ClientSecrets = new List<Secret> { new Secret("this-is-my-secret".Sha256()) },
    AllowedScopes = new List<string>
    {
        StandardScopes.OpenId.Name,
        StandardScopes.Profile.Name,
        StandardScopes.OfflineAccess.Name,
        "my-protected-api"
    },
    RedirectUris = new List<string>
    {
        "http://localhost:5009/signin-oidc",
    }
}

In my MVC application, I use TokenClientto get a token that I can use when accessing the secure API as follows:

var disco = await DiscoveryClient.GetAsync("http://localhost:5010");
var tokenClient = new TokenClient(disco.TokenEndpoint, clientId, clientSecret);
var tokenResponse = await tokenClient.RequestClientCredentialsAsync("hrmts-test-candidate-api-scope");

This works fine, but I am requesting new tokens from Identity Server for each request, which is probably not a good idea.

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Answer 1

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public class ServerTokenComponent
{
    private TokenResponse Token { get; set; }
    private DateTime ExpiryTime { get; set; }
    public async Task<TokenResponse> GetToken()
    {
        //use token if it exists and is still fresh
        if (Token != null && ExpiryTime > DateTime.UtcNow)
        {    
            return Token;
        }     

        //else get a new token
        var client = new TokenClient("myidpauthority.com","theclientId","thesecret")
        var scopes = "for bar baz";

        var tokenResponse = await client.RequestClientCredentialsAsync(scopes);

        if (tokenResponse.IsError || tokenResponse.IsHttpError)
        {
            throw new SecurityTokenException("Could not retrieve token.");
        }

        //set Token to the new token and set the expiry time to the new expiry time
        Token = tokenResponse;
        ExpiryTime = DateTime.UtcNow.AddSeconds(Token.ExpiresIn);

        //return fresh token
        return Token;
    }
}

Answer 2

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