Support service principal

src/NuGetGallery.Core/Services/CloudBlobClientWrapper.cs

@@ -2,6 +2,8 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Linq;
+using System.Security.Cryptography.X509Certificates;
 using Azure;
 using Azure.Core;
 using Azure.Identity;
@@ -57,6 +59,19 @@ public static CloudBlobClientWrapper UsingMsi(
             return new CloudBlobClientWrapper(storageConnectionString, tokenCredential, readAccessGeoRedundant, requestTimeout);
         }
 
+        public static CloudBlobClientWrapper UsingServicePrincipal(
+            string storageConnectionString, 
+            string appID, 
+            string subjectAlternativeName, 
+            string tenantId, 
+            string authorityHost,
+            bool readAccessGeoRedundant = false,
+            TimeSpan? requestTimeout = null) 
+        {
+            var tokenCredential = GetCredentialUsingServicePrincipal(appID, subjectAlternativeName, tenantId, authorityHost);
+            return new CloudBlobClientWrapper(storageConnectionString, tokenCredential, readAccessGeoRedundant, requestTimeout);
+        }
+
         public ISimpleCloudBlob GetBlobFromUri(Uri uri)
         {
             // For Azure blobs, the query string is assumed to be the SAS token.
@@ -217,5 +232,36 @@ private string GetSecondaryConnectionString()
                 .Replace($"AccountName={primaryAccountName};", $"AccountName={secondaryAccountName};");
             return secondaryConnectionString;
         }
+
+        /// <summary>
+        /// Gets credential using the Service Principal.  If the resource is in a different tenant, this is how to access it.
+        /// The ServicePrincipal needs to be a "Storage Table/Blob/Queue Data Contributor" role on the storage account.  Owner isn't enough.
+        /// </summary>
+        /// <returns>ClientCertificatCredential to be used to communicate with Storage.</returns>
+        private static ClientCertificateCredential GetCredentialUsingServicePrincipal(string appID, string subjectAlternativeName, string tenantId, string authorityHost)
+        {
+            X509Certificate2 clientCert;
+
+            // Azure.Identity library doesn't support referencing cert by Store + Subject name, so we need to load it ourselves.
+            using (X509Store store = new X509Store(StoreName.My, StoreLocation.CurrentUser))
+            {
+                store.Open(OpenFlags.ReadOnly);
+
+                X509Certificate2Collection certs = store.Certificates.Find(X509FindType.FindBySubjectName, subjectAlternativeName, true);
+
+                if (certs.Count == 0)
+                {
+                    throw new InvalidOperationException($"Unable to find certificate with subject name '{subjectAlternativeName}'");
+                }
+
+                // As an exception to comment in GetKeyVaultCertsAsync method, this X509Certificate2 object does not have to be disposed
+                // because it is referencing a platform certificate from CurrentUser certificate store, so no temporary files are created for this object.
+                clientCert = certs.Cast<X509Certificate2>()
+                                .Where(c => c.NotBefore < DateTime.UtcNow && c.NotAfter > DateTime.UtcNow)
+                                .OrderBy(x => x.NotAfter).Last();
+            }
+
+            return new ClientCertificateCredential(tenantId, appID, clientCert, new ClientCertificateCredentialOptions { AuthorityHost = new Uri(authorityHost), SendCertificateChain = true });
+        }
     }
 }