ASP.Net Core Web API unable to connect due to CORS

D

c#
using Asp.Versioning;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.Identity.Web;
using System.Text.Json.Serialization;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddMicrosoftIdentityWebApi(builder.Configuration.GetSection("AzureAd"));

builder.Services.AddControllers().AddJsonOptions(x =>
{
    x.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter());
});
builder.Services.AddProblemDetails();
builder.Services.AddApiVersioning(options =>
{
    options.ReportApiVersions = true;
    options.AssumeDefaultVersionWhenUnspecified = true;
    options.DefaultApiVersion = new ApiVersion(1, 0);
    options.ApiVersionReader = new UrlSegmentApiVersionReader();
}).AddApiExplorer(options =>
{
    options.GroupNameFormat = "'v'VVV";
    options.SubstituteApiVersionInUrl = true;
});

builder.Services.AddCors(options =>
{
    options.AddPolicy("AllowAll", builder =>
    {
        builder
            .WithOrigins("https://localhost:8080", "http://localhost:8081")
            .AllowAnyHeader()
            .AllowAnyMethod();
    });
});


// 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();
}

if (app.Environment.IsStaging() || app.Environment.IsProduction())
{
    app.UseHttpsRedirection();
}

app.UseCors("AllowAll");

app.UseAuthentication();

app.MapControllers();

#pragma warning disable S6966
app.Run();
#pragma warning restore S6966

c#
using Asp.Versioning;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.Identity.Web;
using System.Text.Json.Serialization;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddMicrosoftIdentityWebApi(builder.Configuration.GetSection("AzureAd"));

builder.Services.AddControllers().AddJsonOptions(x =>
{
    x.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter());
});
builder.Services.AddProblemDetails();
builder.Services.AddApiVersioning(options =>
{
    options.ReportApiVersions = true;
    options.AssumeDefaultVersionWhenUnspecified = true;
    options.DefaultApiVersion = new ApiVersion(1, 0);
    options.ApiVersionReader = new UrlSegmentApiVersionReader();
}).AddApiExplorer(options =>
{
    options.GroupNameFormat = "'v'VVV";
    options.SubstituteApiVersionInUrl = true;
});

builder.Services.AddCors(options =>
{
    options.AddPolicy("AllowAll", builder =>
    {
        builder
            .WithOrigins("https://localhost:8080", "http://localhost:8081")
            .AllowAnyHeader()
            .AllowAnyMethod();
    });
});


// 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();
}

if (app.Environment.IsStaging() || app.Environment.IsProduction())
{
    app.UseHttpsRedirection();
}

app.UseCors("AllowAll");

app.UseAuthentication();

app.MapControllers();

#pragma warning disable S6966
app.Run();
#pragma warning restore S6966

c#
using Asp.Versioning;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.Identity.Web;
using System.Text.Json.Serialization;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddMicrosoftIdentityWebApi(builder.Configuration.GetSection("AzureAd"));

builder.Services.AddControllers().AddJsonOptions(x =>
{
    x.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter());
});
builder.Services.AddProblemDetails();
builder.Services.AddApiVersioning(options =>
{
    options.ReportApiVersions = true;
    options.AssumeDefaultVersionWhenUnspecified = true;
    options.DefaultApiVersion = new ApiVersion(1, 0);
    options.ApiVersionReader = new UrlSegmentApiVersionReader();
}).AddApiExplorer(options =>
{
    options.GroupNameFormat = "'v'VVV";
    options.SubstituteApiVersionInUrl = true;
});

builder.Services.AddCors(options =>
{
    options.AddPolicy("AllowAll", builder =>
    {
        builder
            .WithOrigins("https://localhost:8080", "http://localhost:8081")
            .AllowAnyHeader()
            .AllowAnyMethod();
    });
});


// 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();
}

if (app.Environment.IsStaging() || app.Environment.IsProduction())
{
    app.UseHttpsRedirection();
}

app.UseCors("AllowAll");

app.UseAuthentication();

app.MapControllers();

#pragma warning disable S6966
app.Run();
#pragma warning restore S6966

c#
using Asp.Versioning;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.Identity.Web;
using System.Text.Json.Serialization;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddMicrosoftIdentityWebApi(builder.Configuration.GetSection("AzureAd"));

builder.Services.AddControllers().AddJsonOptions(x =>
{
    x.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter());
});
builder.Services.AddProblemDetails();
builder.Services.AddApiVersioning(options =>
{
    options.ReportApiVersions = true;
    options.AssumeDefaultVersionWhenUnspecified = true;
    options.DefaultApiVersion = new ApiVersion(1, 0);
    options.ApiVersionReader = new UrlSegmentApiVersionReader();
}).AddApiExplorer(options =>
{
    options.GroupNameFormat = "'v'VVV";
    options.SubstituteApiVersionInUrl = true;
});

builder.Services.AddCors(options =>
{
    options.AddPolicy("AllowAll", builder =>
    {
        builder
            .WithOrigins("https://localhost:8080", "http://localhost:8081")
            .AllowAnyHeader()
            .AllowAnyMethod();
    });
});


// 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();
}

if (app.Environment.IsStaging() || app.Environment.IsProduction())
{
    app.UseHttpsRedirection();
}

app.UseCors("AllowAll");

app.UseAuthentication();

app.MapControllers();

#pragma warning disable S6966
app.Run();
#pragma warning restore S6966

D

Destination Unknown•4/24/25, 1:27 PM

appsettings.json: nothing really useful

docker-compose.override:

services:
  myProject.api:
    environment:
      - ASPNETCORE_ENVIRONMENT=Development
      - ASPNETCORE_HTTP_PORTS=8080
      - ASPNETCORE_HTTPS_PORTS=8081
    ports:
      - "8080:8080"
      - "8081:8081"

services:
  myProject.api:
    environment:
      - ASPNETCORE_ENVIRONMENT=Development
      - ASPNETCORE_HTTP_PORTS=8080
      - ASPNETCORE_HTTPS_PORTS=8081
    ports:
      - "8080:8080"
      - "8081:8081"

services:
  myProject.api:
    environment:
      - ASPNETCORE_ENVIRONMENT=Development
      - ASPNETCORE_HTTP_PORTS=8080
      - ASPNETCORE_HTTPS_PORTS=8081
    ports:
      - "8080:8080"
      - "8081:8081"

services:
  myProject.api:
    environment:
      - ASPNETCORE_ENVIRONMENT=Development
      - ASPNETCORE_HTTP_PORTS=8080
      - ASPNETCORE_HTTPS_PORTS=8081
    ports:
      - "8080:8080"
      - "8081:8081"

docker-compose.yml

services:
  myProject.api:
    container_name: api
    image: ${DOCKER_REGISTRY-}myProjectapi
    build:
      context: .
      dockerfile: Sample.API/Dockerfile
    ports:
        - "8080:8080"
        - "8081:8081"

services:
  myProject.api:
    container_name: api
    image: ${DOCKER_REGISTRY-}myProjectapi
    build:
      context: .
      dockerfile: Sample.API/Dockerfile
    ports:
        - "8080:8080"
        - "8081:8081"

services:
  myProject.api:
    container_name: api
    image: ${DOCKER_REGISTRY-}myProjectapi
    build:
      context: .
      dockerfile: Sample.API/Dockerfile
    ports:
        - "8080:8080"
        - "8081:8081"

services:
  myProject.api:
    container_name: api
    image: ${DOCKER_REGISTRY-}myProjectapi
    build:
      context: .
      dockerfile: Sample.API/Dockerfile
    ports:
        - "8080:8080"
        - "8081:8081"

D

Destination Unknown•4/24/25, 1:28 PM

Without the CORS stuff, you can remove the following lines of the program.cs;

c#
builder.Services.AddCors(options =>
{
    options.AddPolicy("AllowAll", builder =>
    {
        builder
            .WithOrigins("https://localhost:8080", "http://localhost:8081")
            .AllowAnyHeader()
            .AllowAnyMethod();
    });
});

app.UseCors("AllowAll");

c#
builder.Services.AddCors(options =>
{
    options.AddPolicy("AllowAll", builder =>
    {
        builder
            .WithOrigins("https://localhost:8080", "http://localhost:8081")
            .AllowAnyHeader()
            .AllowAnyMethod();
    });
});

app.UseCors("AllowAll");

c#
builder.Services.AddCors(options =>
{
    options.AddPolicy("AllowAll", builder =>
    {
        builder
            .WithOrigins("https://localhost:8080", "http://localhost:8081")
            .AllowAnyHeader()
            .AllowAnyMethod();
    });
});

app.UseCors("AllowAll");

c#
builder.Services.AddCors(options =>
{
    options.AddPolicy("AllowAll", builder =>
    {
        builder
            .WithOrigins("https://localhost:8080", "http://localhost:8081")
            .AllowAnyHeader()
            .AllowAnyMethod();
    });
});

app.UseCors("AllowAll");

A

Anchy•4/25/25, 9:17 AM

I see you have setup your HTTP port as 8080 and your HTTPS port as 8081, however in your CORS settings you have reversed them

D

Destination Unknown•4/25/25, 10:14 AM

Hey Anchy, thank you for your reply. I would assume you mean this line of code:

.WithOrigins("https://localhost:8080", "http://localhost:8081")

.WithOrigins("https://localhost:8080", "http://localhost:8081")

.WithOrigins("https://localhost:8080", "http://localhost:8081")

.WithOrigins("https://localhost:8080", "http://localhost:8081")

I swapped the 2 but this still gave me the same 'error'

D

Destination Unknown•4/25/25, 10:15 AM

But do i actually need CORS? Because as far as I know, CORS is used when you want to perform HTTP-requests to another domain. In my case everything is local(host).

D

Destination Unknown•4/25/25, 11:03 AM

There is something else wrong. I do not get what it can be...

D

Destination Unknown•4/25/25, 11:07 AM

it was the fockin browser. I used Brave for this, but brave blocked it.

D

Destination Unknown•4/25/25, 11:07 AM

Using Edge works

D

Destination Unknown•4/25/25, 11:07 AM

ARGH

ASP.Net Core Web API unable to connect due to CORS

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