diff --git a/PasswordKeeper.BusinessLogic/Users.cs b/PasswordKeeper.BusinessLogic/Users.cs
index f66b8d9..b4b6399 100644
--- a/PasswordKeeper.BusinessLogic/Users.cs
+++ b/PasswordKeeper.BusinessLogic/Users.cs
@@ -24,7 +24,7 @@ public class Users(PasswordKeeper.DataAccess.Users users)
     }
     
     /// <inheritdoc cref="PasswordKeeper.DataAccess.Users.GetUserById"/>
-    public async Task<UserDto?> GetUserById(int id)
+    public async Task<UserDto?> GetUserById(long id)
     {
         return await users.GetUserById(id);
     }
@@ -113,7 +113,7 @@ public async Task<LoginResult> Login(string username, string password, byte[] jw
             byte []? salt = null;
             userDto = new UserDto
             {
-                UserName = username,
+                Username = username,
                 PasswordHash = HashPassword(password, ref salt),
                 PasswordSalt = Convert.ToBase64String(salt!),
                 IsAdmin = true,
diff --git a/PasswordKeeper.Classes/Passwords.cs b/PasswordKeeper.Classes/Passwords.cs
index 13ddfe6..d1992cb 100644
--- a/PasswordKeeper.Classes/Passwords.cs
+++ b/PasswordKeeper.Classes/Passwords.cs
@@ -154,6 +154,11 @@ public static string CreateMessageString(LoginRejectReason reason)
     /// An error message indicating that the username or password is invalid.
     /// </summary>
     public const string InvalidUsernameOrPassword = "Invalid username or password.";
+    
+    /// <summary>
+    /// An error message indicating that the user already exists.
+    /// </summary>
+    public const string UserAlreadyExists = "User already exists.";
 
     /// <summary>
     /// A read-only dictionary mapping login reject reasons to error messages.
@@ -179,6 +184,7 @@ public static string CreateMessageString(LoginRejectReason reason)
                 FailedToCreateAdminUser),
             new KeyValuePair<LoginRejectReason, string>(LoginRejectReason.InvalidUsernameOrPassword,
                 InvalidUsernameOrPassword),
-            new KeyValuePair<LoginRejectReason, string>(LoginRejectReason.NotFound, string.Empty)
+            new KeyValuePair<LoginRejectReason, string>(LoginRejectReason.NotFound, string.Empty),
+            new KeyValuePair<LoginRejectReason, string>(LoginRejectReason.UserAlreadyExists, UserAlreadyExists),
         ])));
 }
\ No newline at end of file
diff --git a/PasswordKeeper.DAO/User.cs b/PasswordKeeper.DAO/User.cs
index 4e0653a..c736bfe 100644
--- a/PasswordKeeper.DAO/User.cs
+++ b/PasswordKeeper.DAO/User.cs
@@ -13,9 +13,9 @@ public class User : IUser
     /// <inheritdoc cref="IHasId.Id" />
     public long Id { get; set; }
     
-    /// <inheritdoc cref="IUser.UserName" />
+    /// <inheritdoc cref="IUser.Username" />
     [MaxLength(255)]
-    public string UserName { get; set; } = string.Empty;
+    public string Username { get; set; } = string.Empty;
 
     /// <inheritdoc cref="IUser.PasswordHash" />
     [MaxLength(1000)]
diff --git a/PasswordKeeper.DTO/UserDto.cs b/PasswordKeeper.DTO/UserDto.cs
index 1d2fbc5..2610ea6 100644
--- a/PasswordKeeper.DTO/UserDto.cs
+++ b/PasswordKeeper.DTO/UserDto.cs
@@ -11,8 +11,8 @@ public class UserDto : IUser
     /// <inheritdoc cref="IHasId.Id" />
     public long Id { get; set; }
     
-    /// <inheritdoc cref="IUser.UserName" />
-    public string UserName { get; set; } = string.Empty;
+    /// <inheritdoc cref="IUser.Username" />
+    public string Username { get; set; } = string.Empty;
 
     /// <inheritdoc cref="IUser.PasswordHash" />
     [JsonIgnore]
diff --git a/PasswordKeeper.DataAccess/Users.cs b/PasswordKeeper.DataAccess/Users.cs
index 5ce4f7b..070b324 100644
--- a/PasswordKeeper.DataAccess/Users.cs
+++ b/PasswordKeeper.DataAccess/Users.cs
@@ -21,7 +21,7 @@ public class Users(IDbContextFactory<Entities> dbContextFactory, IMapper mapper)
     {
         await using var context = await dbContextFactory.CreateDbContextAsync();
 
-        var user = await context.Users.FirstOrDefaultAsync(user => user.UserName == name);
+        var user = await context.Users.FirstOrDefaultAsync(user => user.Username == name);
 
         return mapper.Map<UserDto?>(user);
     }
@@ -31,7 +31,7 @@ public class Users(IDbContextFactory<Entities> dbContextFactory, IMapper mapper)
     /// </summary>
     /// <param name="id">The user ID to search for.</param>
     /// <returns>The user with the given ID, or null if it doesn't exist.</returns>
-    public async Task<UserDto?> GetUserById(int id)
+    public async Task<UserDto?> GetUserById(long id)
     {
         await using var context = await dbContextFactory.CreateDbContextAsync();
 
@@ -67,7 +67,7 @@ public async Task<bool> UsersExist(bool? admin = null)
     {
         await using var context = await dbContextFactory.CreateDbContextAsync();
         
-        var user = await context.Users.FirstOrDefaultAsync(user => user.UserName == userDto.UserName);
+        var user = await context.Users.FirstOrDefaultAsync(user => user.Username == userDto.Username);
         
         if (user == null)
         {
diff --git a/PasswordKeeper.DatabaseMigrations/Migrations/001_InitialMigration.cs b/PasswordKeeper.DatabaseMigrations/Migrations/001_InitialMigration.cs
index 8fd7bc7..f578f47 100644
--- a/PasswordKeeper.DatabaseMigrations/Migrations/001_InitialMigration.cs
+++ b/PasswordKeeper.DatabaseMigrations/Migrations/001_InitialMigration.cs
@@ -23,7 +23,7 @@ public override void Up()
 
         this.Create.Table(nameof(User)).InSchemaIf(Program.DatabaseName, !isSqlite)
             .WithColumn(nameof(User.Id)).AsInt64().NotNullable().PrimaryKey().Identity()
-            .WithColumn(nameof(User.UserName)).AsString(255).NotNullable().Unique()
+            .WithColumn(nameof(User.Username)).AsString(255).NotNullable().Unique()
             .WithColumn(nameof(User.PasswordHash)).AsString(1000).NotNullable()
             .WithColumn(nameof(User.PasswordSalt)).AsString(1000).NotNullable()
             .WithColumn(nameof(User.IsAdmin)).AsBoolean().NotNullable().WithDefaultValue(false);
diff --git a/PasswordKeeper.DatabaseMigrations/Program.cs b/PasswordKeeper.DatabaseMigrations/Program.cs
index 8adbfc1..5e8d164 100644
--- a/PasswordKeeper.DatabaseMigrations/Program.cs
+++ b/PasswordKeeper.DatabaseMigrations/Program.cs
@@ -50,7 +50,8 @@ public void OnExecute()
         string connectionString;
         if (TestDbName != null)
         {
-            connectionString = $"Data Source=./{TestDbName}.db";
+            // NOTE: Pooling=False is required for SQLite for the database file to be released after migrations!
+            connectionString = $"Data Source=./{TestDbName}.db;Pooling=False;";
             IsTestDb = true;
         }
         else
diff --git a/PasswordKeeper.Interfaces/Enumerations/LoginRejectReason.cs b/PasswordKeeper.Interfaces/Enumerations/LoginRejectReason.cs
index 352c82f..98bc19f 100644
--- a/PasswordKeeper.Interfaces/Enumerations/LoginRejectReason.cs
+++ b/PasswordKeeper.Interfaces/Enumerations/LoginRejectReason.cs
@@ -58,5 +58,10 @@ public enum LoginRejectReason
     /// <summary>
     /// Data related to the user was not found.
     /// </summary>
-    NotFound,
+    NotFound = 10,
+    
+    /// <summary>
+    /// The user already exists.
+    /// </summary>
+    UserAlreadyExists = 11,
 }
\ No newline at end of file
diff --git a/PasswordKeeper.Interfaces/IUser.cs b/PasswordKeeper.Interfaces/IUser.cs
index 7c01950..f5e7df7 100644
--- a/PasswordKeeper.Interfaces/IUser.cs
+++ b/PasswordKeeper.Interfaces/IUser.cs
@@ -8,7 +8,7 @@ public interface IUser : IHasId
     /// <summary>
     /// The name of the user.
     /// </summary>
-    string UserName { get; set; }
+    string Username { get; set; }
     
     /// <summary>
     /// The password of the user.
diff --git a/PasswordKeeper.Server/Controllers/AuthenticationController.cs b/PasswordKeeper.Server/Controllers/AuthenticationController.cs
index 2fedc9a..d80c528 100644
--- a/PasswordKeeper.Server/Controllers/AuthenticationController.cs
+++ b/PasswordKeeper.Server/Controllers/AuthenticationController.cs
@@ -2,6 +2,7 @@
 using Microsoft.AspNetCore.Mvc;
 using PasswordKeeper.BusinessLogic;
 using PasswordKeeper.Classes;
+using PasswordKeeper.DTO;
 using PasswordKeeper.Server.Controllers.Extensions;
 
 namespace PasswordKeeper.Server.Controllers;
@@ -130,12 +131,65 @@ public async Task<IActionResult> UpdateUserName([FromBody] UserChangeRequest use
             return BadRequest(Passwords.UsernameMustBeAtLeast4CharactersLong);
         }
         
-        userDto.UserName = user.Username;
+        userDto.Username = user.Username;
         var result = await users.UpsertUser(userDto);
         
         return result is null ? BadRequest() : Ok(result);
     }
     
+    /// <summary>
+    /// Creates a new user if the requester is admin.
+    /// </summary>
+    /// <param name="user">The user data to create.</param>
+    /// <returns>
+    /// Unauthorized if the requester is not admin, BadRequest if the upsert operation fails,
+    /// otherwise Ok with the created user data.
+    /// </returns>
+    public async Task<IActionResult> CreateUser([FromBody] UserChangeRequest user)
+    {
+        var loggedUser = await users.GetUserById(this.GetLoggedUserId());
+        
+        if (await users.GetUserByName(user.Username) is not null)
+        {
+            return BadRequest(Passwords.UserAlreadyExists);
+        }
+
+        if (loggedUser == null)
+        {
+            return Unauthorized();
+        }
+
+        if (loggedUser.IsAdmin)
+        {
+            if (!Passwords.IsPasswordOk(user.Password, out var message, out _))
+            {
+                return BadRequest(message);
+            }
+            
+            if (user.Username.Length < 4)
+            {
+                return BadRequest(Passwords.UsernameMustBeAtLeast4CharactersLong);
+            }
+            
+            var userDto = new UserDto
+            {
+                Username = user.Username,
+                PasswordHash = string.Empty,
+                PasswordSalt = string.Empty,
+                IsAdmin = false,
+            };
+        
+            var salt = Convert.FromBase64String(userDto.PasswordSalt);
+            userDto.PasswordHash = Users.HashPassword(user.Password, ref salt);
+            userDto.PasswordSalt = Convert.ToBase64String(salt!);
+            var result = await users.UpsertUser(userDto);
+        
+            return result is null ? BadRequest() : Ok(result);
+        }
+
+        return Unauthorized();
+    }
+    
     /// <summary>
     /// An endpoint for testing unauthorized access.
     /// </summary>
diff --git a/PasswordKeeper.Server/Controllers/Extensions/ControllerExtensions.cs b/PasswordKeeper.Server/Controllers/Extensions/ControllerExtensions.cs
index 0a297ef..0ff9d34 100644
--- a/PasswordKeeper.Server/Controllers/Extensions/ControllerExtensions.cs
+++ b/PasswordKeeper.Server/Controllers/Extensions/ControllerExtensions.cs
@@ -14,15 +14,25 @@ public static class ControllerExtensions
     /// <returns>The logged-in user's ID, or -1 if the claim containing the user ID is not found.</returns>
     public static long GetLoggedUserId(this ControllerBase controllerBase)
     {
-        var claim = controllerBase.User.Claims.FirstOrDefault(c => c.Type == ClaimTypes.NameIdentifier && long.TryParse(c.Value, out _));
-        
+        return GetLoggedUserIdFunc(controllerBase);
+    }
+
+    /// <summary>
+    /// A delegate to get the logged-in user's ID. This is called by the <see cref="GetLoggedUserId"/> method.
+    /// </summary>
+    /// <remarks>A delegate is used to allow unit testing.</remarks>
+    public static Func<ControllerBase, long> GetLoggedUserIdFunc = controllerBase =>
+    {
+        var claim = controllerBase.User.Claims.FirstOrDefault(c =>
+            c.Type == ClaimTypes.NameIdentifier && long.TryParse(c.Value, out _));
+
         if (long.TryParse(claim?.Value, out var result))
         {
             return result;
         }
-        
+
         return -1;
-    }
+    }; 
     
     /// <summary>
     /// Gets the logged-in user's name.
@@ -30,6 +40,15 @@ public static long GetLoggedUserId(this ControllerBase controllerBase)
     /// <returns>The logged-in user's name, or an empty string if the user is not logged in.</returns>
     public static string GetLoggedUserName(this ControllerBase controllerBase)
     {
-        return controllerBase.User.Identity?.Name ?? string.Empty;
+        return GetLoggedUserNameFunc(controllerBase);
     }
+    
+    /// <summary>
+    /// A delegate to get the logged-in user's name. This is called by the <see cref="GetLoggedUserName"/> method.
+    /// </summary>
+    /// <remarks>A delegate is used to allow unit testing.</remarks>
+    public static Func<ControllerBase, string> GetLoggedUserNameFunc = controllerBase =>
+    {
+        return controllerBase.User.Identity?.Name ?? string.Empty;
+    };
 }
\ No newline at end of file
diff --git a/PasswordKeeper.Tests/ControllerTests.cs b/PasswordKeeper.Tests/ControllerTests.cs
index f961a15..87eee0c 100644
--- a/PasswordKeeper.Tests/ControllerTests.cs
+++ b/PasswordKeeper.Tests/ControllerTests.cs
@@ -1,8 +1,10 @@
 using Microsoft.AspNetCore.Mvc;
 using PasswordKeeper.Classes;
 using PasswordKeeper.DatabaseMigrations;
+using PasswordKeeper.DTO;
 using PasswordKeeper.Interfaces.Enumerations;
 using PasswordKeeper.Server.Controllers;
+using PasswordKeeper.Server.Controllers.Extensions;
 
 namespace PasswordKeeper.Tests;
 
@@ -20,15 +22,18 @@ public void Setup()
         Helpers.DeleteDatabase(nameof(ControllerTests));
         Program.Main([$"-t {nameof(ControllerTests)}",]);
         Server.Program.GetJwtKey = Helpers.GetJwtKey;
+        ControllerExtensions.GetLoggedUserIdFunc = @base => 1;
+        ControllerExtensions.GetLoggedUserNameFunc = @base => "firsUserIsAdmin";
     }
     
     /// <summary>
-    /// Tests the authentication controller.
+    /// Tests the AuthenticationController.Login action.
     /// </summary>
     [Test]
-    public async Task AuthenticationControllerTest()
+    public async Task AuthenticationControllerLoginTest()
     {
-        var dataAccess = new PasswordKeeper.DataAccess.Users(Helpers.GetMockDbContextFactory(nameof(ControllerTests)), Helpers.CreateMapper());
+        var dbContextFactory = Helpers.GetMockDbContextFactory(nameof(ControllerTests));
+        var dataAccess = new PasswordKeeper.DataAccess.Users(dbContextFactory, Helpers.CreateMapper());
         var businessLogic = new PasswordKeeper.BusinessLogic.Users(dataAccess);
         var controller = new AuthenticationController(businessLogic);
         var loginData = new AuthenticationController.UserLogin("firsUserIsAdmin", "password");
@@ -43,5 +48,30 @@ public async Task AuthenticationControllerTest()
         loginData = new AuthenticationController.UserLogin("firsUserIsAdmin", "Pa1sword%");
         result = await controller.Login(loginData);
         Assert.That(result, Is.TypeOf<OkObjectResult>());
+        await dbContextFactory.DisposeAsync();
+    }
+    
+    /// <summary>
+    /// Tests the AuthenticationController.CreateUser action.
+    /// </summary>
+    [Test]
+    public async Task ControllerCreateUserTest()
+    {
+        var dbContextFactory = Helpers.GetMockDbContextFactory(nameof(ControllerTests));
+        var dataAccess = new PasswordKeeper.DataAccess.Users(dbContextFactory, Helpers.CreateMapper());
+        var businessLogic = new PasswordKeeper.BusinessLogic.Users(dataAccess);
+        var controller = new AuthenticationController(businessLogic);
+        var loginData = new AuthenticationController.UserLogin("firsUserIsAdmin", "Pa1sword%");
+        await controller.Login(loginData);
+        
+        var user = new AuthenticationController.UserChangeRequest(0, "normalUser", "pAssw0rd_");
+
+        var createdUser = await controller.CreateUser(user);
+        
+        Assert.That(createdUser, Is.TypeOf<OkObjectResult>());
+        var userDto = ((OkObjectResult)createdUser).Value as UserDto;
+        Assert.That(userDto, Is.TypeOf<UserDto>());
+        Assert.That(userDto.Username, Is.EqualTo("normalUser"));
+        await dbContextFactory.DisposeAsync();
     }
 }
\ No newline at end of file
diff --git a/PasswordKeeper.Tests/Helpers.cs b/PasswordKeeper.Tests/Helpers.cs
index 2b88cb2..e9e6c85 100644
--- a/PasswordKeeper.Tests/Helpers.cs
+++ b/PasswordKeeper.Tests/Helpers.cs
@@ -19,7 +19,7 @@ public static class Helpers
     public static Entities GetMemoryContext(string testClassName)
     {
         var options = new DbContextOptionsBuilder<Entities>()
-            .UseSqlite($"Data Source=./{testClassName}.db")
+            .UseSqlite($"Data Source=./{testClassName}.db;Pooling=False;")
             .Options;
         
         return new Entities(options);
@@ -30,11 +30,11 @@ public static Entities GetMemoryContext(string testClassName)
     /// </summary>
     /// <param name="testClassName">The name of the test class.</param>
     /// <returns>The database context.</returns>
-    public static IDbContextFactory<Entities> GetMockDbContextFactory(string testClassName)
+    public static IDisposableContextFactory<Entities> GetMockDbContextFactory(string testClassName)
     {
         return new MockDbContextFactory(testClassName);
     }
-    
+
     /// <summary>
     /// Deletes the database file.
     /// </summary>
@@ -47,7 +47,7 @@ public static void DeleteDatabase(string testClassName)
             File.Delete(dbFile);
         }
     }
-    
+
     /// <summary>
     /// Creates an instance to a class implementing the <see cref="IMapper"/> interface.
     /// </summary>
diff --git a/PasswordKeeper.Tests/IDisposableContextFactory.cs b/PasswordKeeper.Tests/IDisposableContextFactory.cs
new file mode 100644
index 0000000..234156f
--- /dev/null
+++ b/PasswordKeeper.Tests/IDisposableContextFactory.cs
@@ -0,0 +1,13 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace PasswordKeeper.Tests;
+
+/// <summary>
+/// A disposable database context factory.
+/// </summary>
+/// <typeparam name="T">The type of the database context.</typeparam>
+/// <seealso cref="IDbContextFactory{T}" />
+/// <seealso cref="IDisposable" />
+/// <seealso cref="IAsyncDisposable" />
+public interface IDisposableContextFactory<T> : IDbContextFactory<T>, IDisposable, IAsyncDisposable 
+    where T : DbContext;
\ No newline at end of file
diff --git a/PasswordKeeper.Tests/MockDbContextFactory.cs b/PasswordKeeper.Tests/MockDbContextFactory.cs
index 46096a5..6729fe4 100644
--- a/PasswordKeeper.Tests/MockDbContextFactory.cs
+++ b/PasswordKeeper.Tests/MockDbContextFactory.cs
@@ -8,8 +8,10 @@ namespace PasswordKeeper.Tests;
 /// </summary>
 /// <param name="testClassName">The name of the test class.</param>
 /// <seealso cref="IDbContextFactory{Entities}" />
-public class MockDbContextFactory(string testClassName) : IDbContextFactory<Entities>
+public class MockDbContextFactory(string testClassName) : IDisposableContextFactory<Entities>
 {
+    private Entities? context;
+    
     /// <summary>
     /// Creates a new SQLite database context.
     /// </summary>
@@ -17,9 +19,28 @@ public class MockDbContextFactory(string testClassName) : IDbContextFactory<Enti
     public Entities CreateDbContext()
     {
         var options = new DbContextOptionsBuilder<Entities>()
-            .UseSqlite($"Data Source=./{testClassName}.db")
+            .UseSqlite($"Data Source=./{testClassName}.db;Pooling=False;")
             .Options;
         
-        return new Entities(options);
+        context = new Entities(options);
+
+        return context;
+    }
+
+    /// <inheritdoc cref="IDisposable.Dispose" />
+    public void Dispose()
+    {
+        context?.Dispose();
+        context = null;
+    }
+
+    /// <inheritdoc cref="IAsyncDisposable.DisposeAsync" />
+    public async ValueTask DisposeAsync()
+    {
+        if (context != null)
+        {
+            await context.DisposeAsync();
+            context = null;
+        }
     }
 }
\ No newline at end of file