Add TryAddScheme (#14448)

src/Http/Authentication.Abstractions/ref/Microsoft.AspNetCore.Authentication.Abstractions.netcoreapp.cs

@@ -149,6 +149,7 @@ namespace Microsoft.AspNetCore.Authentication
         System.Threading.Tasks.Task<System.Collections.Generic.IEnumerable<Microsoft.AspNetCore.Authentication.AuthenticationScheme>> GetRequestHandlerSchemesAsync();
         System.Threading.Tasks.Task<Microsoft.AspNetCore.Authentication.AuthenticationScheme> GetSchemeAsync(string name);
         void RemoveScheme(string name);
+        bool TryAddScheme(Microsoft.AspNetCore.Authentication.AuthenticationScheme scheme) { throw null; }
     }
     public partial interface IAuthenticationService
     {

src/Http/Authentication.Abstractions/src/IAuthenticationSchemeProvider.cs

@@ -71,6 +71,23 @@ namespace Microsoft.AspNetCore.Authentication
         /// <param name="scheme">The scheme.</param>
         void AddScheme(AuthenticationScheme scheme);
 
+        /// <summary>
+        /// Registers a scheme for use by <see cref="IAuthenticationService"/>. 
+        /// </summary>
+        /// <param name="scheme">The scheme.</param>
+        /// <returns>true if the scheme was added successfully.</returns>
+        bool TryAddScheme(AuthenticationScheme scheme)
+        {
+            try
+            {
+                AddScheme(scheme);
+                return true;
+            }
+            catch {
+                return false;
+            }
+        }
+
         /// <summary>
         /// Removes a scheme, preventing it from being used by <see cref="IAuthenticationService"/>.
         /// </summary>

src/Http/Authentication.Core/ref/Microsoft.AspNetCore.Authentication.Core.netcoreapp.cs

@@ -30,6 +30,7 @@ namespace Microsoft.AspNetCore.Authentication
         public virtual System.Threading.Tasks.Task<System.Collections.Generic.IEnumerable<Microsoft.AspNetCore.Authentication.AuthenticationScheme>> GetRequestHandlerSchemesAsync() { throw null; }
         public virtual System.Threading.Tasks.Task<Microsoft.AspNetCore.Authentication.AuthenticationScheme> GetSchemeAsync(string name) { throw null; }
         public virtual void RemoveScheme(string name) { }
+        public virtual bool TryAddScheme(Microsoft.AspNetCore.Authentication.AuthenticationScheme scheme) { throw null; }
     }
     public partial class AuthenticationService : Microsoft.AspNetCore.Authentication.IAuthenticationService
     {

src/Http/Authentication.Core/src/AuthenticationSchemeProvider.cs

@@ -133,17 +133,18 @@ namespace Microsoft.AspNetCore.Authentication
         /// Registers a scheme for use by <see cref="IAuthenticationService"/>. 
         /// </summary>
         /// <param name="scheme">The scheme.</param>
-        public virtual void AddScheme(AuthenticationScheme scheme)
+        /// <returns>true if the scheme was added successfully.</returns>
+        public virtual bool TryAddScheme(AuthenticationScheme scheme)
         {
             if (_schemes.ContainsKey(scheme.Name))
             {
-                throw new InvalidOperationException("Scheme already exists: " + scheme.Name);
+                return false;
             }
             lock (_lock)
             {
                 if (_schemes.ContainsKey(scheme.Name))
                 {
-                    throw new InvalidOperationException("Scheme already exists: " + scheme.Name);
+                    return false;
                 }
                 if (typeof(IAuthenticationRequestHandler).IsAssignableFrom(scheme.HandlerType))
                 {
@@ -152,6 +153,26 @@ namespace Microsoft.AspNetCore.Authentication
                 }
                 _schemes[scheme.Name] = scheme;
                 _schemesCopy = _schemes.Values.ToArray();
+                return true;
+            }
+        }
+
+        /// <summary>
+        /// Registers a scheme for use by <see cref="IAuthenticationService"/>. 
+        /// </summary>
+        /// <param name="scheme">The scheme.</param>
+        public virtual void AddScheme(AuthenticationScheme scheme)
+        {
+            if (_schemes.ContainsKey(scheme.Name))
+            {
+                throw new InvalidOperationException("Scheme already exists: " + scheme.Name);
+            }
+            lock (_lock)
+            {
+                if (!TryAddScheme(scheme))
+                {
+                    throw new InvalidOperationException("Scheme already exists: " + scheme.Name);
+                }
             }
         }
 

src/Http/Authentication.Core/test/AuthenticationSchemeProviderTests.cs

@@ -133,6 +133,23 @@ namespace Microsoft.AspNetCore.Authentication
             Assert.Contains("Scheme already exists: signin", error.Message);
         }
 
+        [Fact]
+        public void CanSafelyTryAddSchemes()
+        {
+            var services = new ServiceCollection().AddOptions().AddAuthenticationCore(o =>
+            {
+            }).BuildServiceProvider();
+
+            var o = services.GetRequiredService<IAuthenticationSchemeProvider>();
+            Assert.True(o.TryAddScheme(new AuthenticationScheme("signin", "whatever", typeof(Handler))));
+            Assert.True(o.TryAddScheme(new AuthenticationScheme("signin2", "whatever", typeof(Handler))));
+            Assert.False(o.TryAddScheme(new AuthenticationScheme("signin", "whatever", typeof(Handler))));
+            Assert.True(o.TryAddScheme(new AuthenticationScheme("signin3", "whatever", typeof(Handler))));
+            Assert.False(o.TryAddScheme(new AuthenticationScheme("signin2", "whatever", typeof(Handler))));
+            o.RemoveScheme("signin2");
+            Assert.True(o.TryAddScheme(new AuthenticationScheme("signin2", "whatever", typeof(Handler))));
+        }
+
         [Fact]
         public async Task LookupUsesProvidedStringComparer()
         {