arrayinitializer.cs

        private OAuthOptions GitHubOptions =>

    new OAuthOptions
    {
        AuthenticationScheme = "GitHub",
        DisplayName = "GitHub",
        ClientId = Configuration["GitHub:ClientId"],
        ClientSecret = Configuration["GitHub:ClientSecret"],
        CallbackPath = new PathString("/signin-github"),
        AuthorizationEndpoint = "https://github.com/login/oauth/authorize",
        TokenEndpoint = "https://github.com/login/oauth/access_token",
        UserInformationEndpoint = "https://api.github.com/user",
        ClaimsIssuer = "OAuth2-Github",
        Scope = { "user", "repo" },
        SaveTokensAsClaims = true,

        // Retrieving user information is unique to each provider.
        Events = new OAuthEvents
        {
            OnCreatingTicket = async context => { await CreatingGitHubAuthTicket(context); }
        }
    };

gitHubOptions.Scope.Add.cs

private OAuthOptions GitHubOptions
{
    get
    {
        var gitHubOptions = new OAuthOptions
        {
            AuthenticationScheme = "GitHub",
            DisplayName = "GitHub",
            ClientId = Configuration["GitHub:ClientId"],
            ClientSecret = Configuration["GitHub:ClientSecret"],
            CallbackPath = new PathString("/signin-github"),
            AuthorizationEndpoint = "https://github.com/login/oauth/authorize",
            TokenEndpoint = "https://github.com/login/oauth/access_token",
            UserInformationEndpoint = "https://api.github.com/user",
            ClaimsIssuer = "OAuth2-Github",
            SaveTokensAsClaims = true,

            // Retrieving user information is unique to each provider.
            Events = new OAuthEvents
            {
                OnCreatingTicket = async context => { await CreatingGitHubAuthTicket(context); }
            }
        };
        gitHubOptions.Scope.Add("user");
        gitHubOptions.Scope.Add("repo");
        return gitHubOptions;
    }
}