Simplify authentication in the web application

[tidyui]

Add middleware as described in the following documentation article to the core framework:

https://piranhacms.org/docs/tutorials/securing-pages

[tidyui]

Current solution

The manual way (as described in the article referenced above) includes

1. Adding Policies & Claims to ASP.NET in ConfigureServices
2. Adding the claims to the Permission Manager in Configure so they will show up in Piranha
3. Adding a custom middleware component in Configure for handling redirects.

This gives the following code:

ConfigureServices

public void ConfigureServices(IServiceCollection services)
{
    ...

    // Add custom policies
    services.AddAuthorization(o =>
    {
        // Read secured posts
        o.AddPolicy("ReadSecuredPosts", policy =>
        {
            policy.RequireClaim("ReadSecuredPosts", "ReadSecuredPosts");
        });
    });
}

Configure

public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IApi api)
{
    ...

    // Custom permissions
    App.Permissions["App"].Add(new Piranha.Security.PermissionItem
    {
        Title = "Read secured posts",
        Name = "ReadSecuredPosts"
    });

    // Custom middleware that checks for status 401
    app.Use(async (ctx, next) =>
    {
        await next();

        if (ctx.Response.StatusCode == 401)
        {
            ctx.Response.Redirect("/login");
        }
    });

   ...
}

Proposed solution

Adding a new helper method to the PiranhaServiceBuilder that simplifies the setup for all basic scenarios. The manual code above would be replaced by the following:

ConfigureServices

public void ConfigureServices(IServiceCollection services)
{
    services.AddPiranha(options =>
    {
        ...
        
        options.UseSecurity(o =>
        {
            o.UsePermission("ReadSecuredPosts");
        });
    });
}

Simplifications

The method UsePermission will perform the following:

1. Add a new Policy to ASP.NET with the given name
2. Require a single claim with the same name as the Policy
3. Add a new item into Piranha.App.Permissions with the same name (and optional title)

This means that it won't be supported adding composite policies this way that require several different claims. But as the whole purpose of these methods are to simplify we think this is ok.