I have a blazor web assembly which fetches from an external API built on ASP.NET Core which I do not have access to. I can perform get requests, but cannot perform post requests. I get the following error when I do.
Access to fetch at 'http://external:9000/User/Create' from origin 'http://localhost:56138' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.
The author of the api confirms he enabled cors to allow any header in his startup and also suggested I do the same but this did not fix the issue. I confirmed from the debugger I am sending the right data format the endpoint requires and I am also running on http scheme same as the web service.
This is the client configuration in program.cs
builder.Services.AddScoped(sp => new HttpClient { BaseAddress = new Uri("http://external:9000/") });
builder.Services.AddCors(policy =>
{
policy.AddPolicy("_myAllowSpecificOrigins", builder => builder.WithOrigins("http://external:9000/")
.AllowAnyMethod()
.AllowAnyHeader()
.AllowCredentials());
});
This is how I post
var dataJson = JsonConvert.SerializeObject(application);
var stringContent = new StringContent(dataJson, Encoding.UTF8, "application/json");
var response = await _httpClient.PostAsync($"User/Create", stringContent);
I have read this is a common problem with blazor assembly, I'm not entirely sure of what I read. I am currently trying to move the project to blazor server to see if it would work, but I would prefer it on web assembly.
.AddCors(...)
on the client is of little use. It looks like the other author may allow any Header but not any Method. The problem is on the server.