HookingOwinNotifications.cs

// startup.auth.cs
{ ….

var openIdConnectAuthenticationOptions = 
    new OpenIdConnectAuthenticationOptions
    {
        Authentication Type = OpenIdConnectAuthenticationDefaults.AuthenticationType,
        Authority = authority,
        ClientId = client ID,

        Notifications =
            new OpenIdConnectAuthenticationNotifications
            {
                AuthorizationCodeReceived = AuthorizationCodeReceived,
                AuthenticationFailed = AuthenticationFailed,
                MessageReceived = MessageReceived,                   
 
                // 'parameter=value',  will be added to the query string.
                RedirectToIdentityProvider = (notification) => 
                {
                    notification.ProtocolMessage.Parameters["parameter"] = "value";
                    return Task.FromResult(0);
                },
                SecurityTokenReceived = SecurityTokenReceived,
                SecurityTokenValidated = SecurityTokenValidated,
            },
    };
 
    app.UseOpenIdConnectAuthentication(openIdConnectAuthenticationOptions);

….}

public static Task AuthorizationCodeReceived(AuthorizationCodeReceivedNotification notification)
{
    return Task.FromResult<object>(null);
}

public static Task Authentication Failed(AuthenticationFailedNotification<OpenIdConnectMessage, OpenIdConnectAuthenticationOptions> notification)
{
    return Task.FromResult<object>(null);
}

public static Task MessageReceived(MessageReceivedNotification<OpenIdConnectMessage, OpenIdConnectAuthenticationOptions> notification)
{
    return Task.FromResult<object>(null);
}
 
public static Task SecurityTokenReceived(SecurityTokenReceivedNotification<OpenIdConnectMessage, OpenIdConnectAuthenticationOptions> notification)
{
    return Task.FromResult<object>(null);
}
 
public static Task SecurityTokenValidated(SecurityTokenValidatedNotification<OpenIdConnectMessage, OpenIdConnectAuthenticationOptions> notification)
{
    return Task.FromResult<object>(null);
}