Blazor报错“scheme already exists: addidentities”排查求助

问题出在你同时配置了AddAuthentication().AddIdentityCookies()和AddIdentity<ApplicationUser, IdentityRole>()——这两个操作都会注册Identity相关的认证Scheme，导致重复冲突。AddIdentity内部已经自动完成了认证Cookie方案的配置，不需要再单独调用AddIdentityCookies。

修正后的启动代码如下：

using Microsoft.AspNetCore.Components.Authorization;
using Microsoft.AspNetCore.Identity;
using Microsoft.EntityFrameworkCore;
using Swamp.Components;
using Swamp.Components.Account;
using Swamp.Data;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
builder.Services.AddRazorComponents()
    .AddInteractiveServerComponents();

builder.Services.AddCascadingAuthenticationState();
builder.Services.AddScoped<IdentityUserAccessor>();
builder.Services.AddScoped<IdentityRedirectManager>();
builder.Services.AddScoped<AuthenticationStateProvider, IdentityRevalidatingAuthenticationStateProvider>();

var connectionString = builder.Configuration.GetConnectionString("DefaultConnection") ?? throw new InvalidOperationException("Connection string 'DefaultConnection' not found.");

builder.Services.AddDbContextFactory<ApplicationDbContext>(options =>
    options.UseSqlServer(connectionString));

builder.Services.AddQuickGridEntityFrameworkAdapter();

// 移除重复的AddAuthentication配置，AddIdentity会自动处理认证方案
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlServer(connectionString));

builder.Services.AddDatabaseDeveloperPageExceptionFilter();

builder.Services.AddIdentity<ApplicationUser, IdentityRole>()
    .AddUserManager<UserManagerExtension>()
    .AddEntityFrameworkStores<ApplicationDbContext>()
    .AddSignInManager()
    .AddDefaultTokenProviders();

builder.Services.AddServerSideBlazor().AddCircuitOptions(x => x.DetailedErrors = true);

builder.Services.AddSingleton<IEmailSender<ApplicationUser>, IdentityNoOpEmailSender>();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.UseMigrationsEndPoint();
}
else
{
    app.UseExceptionHandler("/Error", createScopeForErrors: true);
    app.UseHsts();
    app.UseMigrationsEndPoint();
}

app.UseHttpsRedirection();

app.UseStaticFiles();
app.UseAntiforgery();

app.MapRazorComponents<App>()
    .AddInteractiveServerRenderMode();

// Add additional endpoints required by the Identity /Account Razor components.
app.MapAdditionalIdentityEndpoints();

app.Run();

注：代码中重复调用的AddQuickGridEntityFrameworkAdapter()可以保留一处，减少冗余配置。

内容的提问来源于stack exchange，提问作者rose-marie paradis