Fix stale renewal check and ACME DNS validation race

src/WebAppSSLManager/AzureHelper.cs

@@ -136,8 +136,11 @@ public static async Task<bool> NeedsNewCertificateAsync()
         {
             ResourceConfiguration resource = await GetResourceConfigurationAsync();
 
+            // Not filtering by issuer here: Let's Encrypt rotates its intermediate CA name over time
+            // (was "Let's Encrypt Authority X3", then "R3", now "R11"/"R12"/"R13"/"YR1", etc.), so any
+            // hardcoded issuer match goes stale. ExistingCertificates is already scoped to this hostname
+            // by GetResourceConfigurationAsync, so picking the latest-expiring one here is sufficient.
             IAppServiceCertificate existingCert = resource.ExistingCertificates?
-                                                            .Where(c => c.Issuer.Contains(Constants.DefaultCA))
                                                             .OrderByDescending(c => c.ExpirationDate)
                                                             .FirstOrDefault();
 

src/WebAppSSLManager/CertificatesHelper.cs

@@ -125,6 +125,13 @@ public static async Task<bool> GetCertificateAsync()
             await AzureHelper.RemoveDNSVerificationTXTRecord(recordName); //to be sure we start clean
             await AzureHelper.CreateDNSVerificationTXTRecord(recordName, dnsTxt);
 
+            // Validating immediately after creating the TXT record races Azure DNS propagation: Let's
+            // Encrypt can check before the record is live, which fails the challenge and flips the
+            // authorization out of "pending" - so every retry after that first failure errors with
+            // "authorization must be pending" instead of actually retrying. Give DNS time to propagate first.
+            _logger.LogInformation($"   Waiting {Settings.WaitTimeBeforeValidate.TotalSeconds}s for DNS propagation before validating...");
+            await Task.Delay(Settings.WaitTimeBeforeValidate);
+
             _logger.LogInformation($"   Validating DNS authorization challenge. Can take up to 90 seconds...");
             var validatedChallege = await dnsChallenge.Validate();
             var waitUntil = DateTime.Now.AddSeconds(90);

src/WebAppSSLManager/Models/Constants.cs

@@ -13,5 +13,6 @@ public class Constants
         public const string DefaultCA = "Let's Encrypt Authority";
         public const int DefaultBatchSize = 0;
         public static readonly TimeSpan DefaultTimeBeforeExpiryToRenewCertificate = TimeSpan.FromDays(30);
+        public static readonly TimeSpan DefaultWaitTimeBeforeValidate = TimeSpan.FromSeconds(15);
     }
 }

src/WebAppSSLManager/Models/Settings.cs

@@ -18,6 +18,7 @@ public static class Settings
         public static bool UseStaging { get; private set; }
         public static int BatchSize { get; private set; }
         public static TimeSpan TimeBeforeExpiryToRenew { get; private set; }
+        public static TimeSpan WaitTimeBeforeValidate { get; private set; }
 
         public static void Init(ILogger logger)
         {
@@ -97,6 +98,14 @@ public static void Init(ILogger logger)
                 _logger.LogWarning("TimeBeforeExpiryToRenew environment variable is null or invalid. Reverting to default");
                 TimeBeforeExpiryToRenew = Constants.DefaultTimeBeforeExpiryToRenewCertificate;
             }
+
+            if (int.TryParse(Environment.GetEnvironmentVariable("WaitTimeBeforeValidateInSeconds"), out int waitSeconds) && waitSeconds >= 0)
+                WaitTimeBeforeValidate = TimeSpan.FromSeconds(waitSeconds);
+            else
+            {
+                _logger.LogWarning("WaitTimeBeforeValidateInSeconds environment variable is null or invalid. Reverting to default");
+                WaitTimeBeforeValidate = Constants.DefaultWaitTimeBeforeValidate;
+            }
         }
     }
 }