feat(deployment): add secure Linux runtime (#17)

src/FinalFactory.Rendezvous.Server/Provisioning/SecretProviders.cs

@@ -40,18 +40,32 @@ internal sealed class SecretMaterial : IDisposable
 
 internal sealed class EnvironmentSecretProvider : ISecretProvider
 {
-    private const string Prefix = "env:";
+    private const string EnvironmentPrefix = "env:";
+    private const string FilePrefix = "file:";
+    private const int MaximumSecretBytes = 4096;
 
     public bool TryGetSecret(string reference, out SecretMaterial? secret)
     {
         secret = null;
-        if (!reference.StartsWith(Prefix, StringComparison.Ordinal)
-            || reference.Length == Prefix.Length)
+        if (reference.StartsWith(EnvironmentPrefix, StringComparison.Ordinal)
+            && reference.Length > EnvironmentPrefix.Length)
         {
-            return false;
+            return TryGetEnvironmentSecret(reference[EnvironmentPrefix.Length..], out secret);
         }
 
-        string? encoded = Environment.GetEnvironmentVariable(reference[Prefix.Length..]);
+        if (reference.StartsWith(FilePrefix, StringComparison.Ordinal)
+            && reference.Length > FilePrefix.Length)
+        {
+            return TryGetFileSecret(reference[FilePrefix.Length..], out secret);
+        }
+
+        return false;
+    }
+
+    private static bool TryGetEnvironmentSecret(string variableName, out SecretMaterial? secret)
+    {
+        secret = null;
+        string? encoded = Environment.GetEnvironmentVariable(variableName);
         if (string.IsNullOrEmpty(encoded))
         {
             return false;
@@ -60,6 +74,12 @@ internal sealed class EnvironmentSecretProvider : ISecretProvider
         try
         {
             byte[] bytes = Convert.FromBase64String(encoded);
+            if (bytes.Length is 0 or > MaximumSecretBytes)
+            {
+                CryptographicOperations.ZeroMemory(bytes);
+                return false;
+            }
+
             secret = new SecretMaterial(bytes);
             CryptographicOperations.ZeroMemory(bytes);
             return true;
@@ -69,6 +89,47 @@ internal sealed class EnvironmentSecretProvider : ISecretProvider
             return false;
         }
     }
+
+    private static bool TryGetFileSecret(string path, out SecretMaterial? secret)
+    {
+        secret = null;
+        byte[]? bytes = null;
+        try
+        {
+            FileInfo file = new(path);
+            if (!file.Exists
+                || !Path.IsPathFullyQualified(path)
+                || file.LinkTarget is not null
+                || file.Length is <= 0 or > MaximumSecretBytes)
+            {
+                return false;
+            }
+
+            bytes = File.ReadAllBytes(path);
+            if (bytes.Length is 0 or > MaximumSecretBytes)
+            {
+                return false;
+            }
+
+            secret = new SecretMaterial(bytes);
+            return true;
+        }
+        catch (Exception exception) when (exception is IOException
+                                           or UnauthorizedAccessException
+                                           or ArgumentException
+                                           or NotSupportedException
+                                           or System.Security.SecurityException)
+        {
+            return false;
+        }
+        finally
+        {
+            if (bytes is not null)
+            {
+                CryptographicOperations.ZeroMemory(bytes);
+            }
+        }
+    }
 }
 
 internal sealed class EphemeralDevelopmentSecretProvider : ISecretProvider, IDisposable