Take a look at this thread :)

Thanks to Andy Butland and his blog article Customising the Umbraco Pipeline.

This is how to do it for Cors:

Create a PipelineFilter:

public CorsPipelineFilter() : base(nameof(CorsPipelineFilter))
{
    PostPipeline = app =>
    {
        app.UseCors(policy => policy
            .AllowAnyMethod()
            .AllowAnyHeader()
            .AllowAnyOrigin());

        //Also works
        //app.UseCors(policy => policy.WithOrigins("http://localhost:36261"));
    };
}

Add filter to Pipeline:

public class ConfigureCorsOptions : IConfigureOptions<UmbracoPipelineOptions>
{
    public void Configure(UmbracoPipelineOptions options)
    {
        options.AddFilter(new CorsPipelineFilter());
    }
}

in Startup in ConfigureServices method:

services.ConfigureOptions<ConfigureCorsOptions>();
services.AddCors();

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