Program.cs

using FirebaseAdmin;
using Google.Apis.Auth.OAuth2;
using Microsoft.AspNetCore.Builder.Extensions;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.

builder.Services.AddControllers();
// Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseSwagger();
    app.UseSwaggerUI();
}

FirebaseApp.Create(new AppOptions()
{
    Credential = GoogleCredential.FromFile(Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "pushnotification-firebase-adminsdk.json")),
});

app.UseHttpsRedirection();

app.UseAuthorization();

app.MapControllers();

app.Run();