add oauth or something

MareSynchronosServer/MareSynchronosShared/RequirementHandlers/ExistingUserRequirementHandler.cs

@@ -0,0 +1,30 @@
+using MareSynchronosShared.Data;
+using MareSynchronosShared.Utils;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+using StackExchange.Redis.Extensions.Core.Abstractions;
+
+namespace MareSynchronosShared.RequirementHandlers;
+public class ExistingUserRequirementHandler : AuthorizationHandler<ExistingUserRequirement>
+{
+    private readonly MareDbContext _dbContext;
+    private readonly ILogger<UserRequirementHandler> _logger;
+
+    public ExistingUserRequirementHandler(MareDbContext dbContext, ILogger<UserRequirementHandler> logger)
+    {
+        _dbContext = dbContext;
+        _logger = logger;
+    }
+
+    protected override async Task HandleRequirementAsync(AuthorizationHandlerContext context, ExistingUserRequirement requirement)
+    {
+        var uid = context.User.Claims.SingleOrDefault(g => string.Equals(g.Type, MareClaimTypes.Uid, StringComparison.Ordinal))?.Value;
+        if (uid == null) context.Fail();
+
+        var user = await _dbContext.Users.AsNoTracking().SingleOrDefaultAsync(b => b.UID == uid).ConfigureAwait(false);
+        if (user == null) context.Fail();
+
+        context.Succeed(requirement);
+    }
+}