CryptographicException when deploying on private stamp.

On private deployment, I see following exception. May be linked to https://github.com/Azure/azure-webjobs-sdk-script/issues/1832 but this is on protect, not unprotect.
```
System.Security.Cryptography.CryptographicException : An error occurred while trying to encrypt the provided data. Refer to the inner exception for more information. ---> System.InvalidOperationException : The key ring does not contain a valid default protection key. The data protection system cannot create a new key because auto-generation of keys is disabled.
at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRingProvider.CreateCacheableKeyRingCore(DateTimeOffset now,IKey keyJustAdded)
at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRingProvider.Microsoft.AspNetCore.DataProtection.KeyManagement.Internal.ICacheableKeyRingProvider.GetCacheableKeyRing(DateTimeOffset now)
at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRingProvider.GetCurrentKeyRingCore(DateTime utcNow)
at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRingProvider.GetCurrentKeyRing()
at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRingBasedDataProtector.Protect(Byte[] plaintext)
End of inner exception
at Microsoft.AspNetCore.DataProtection.KeyManagement.KeyRingBasedDataProtector.Protect(Byte[] plaintext)
at Microsoft.AspNetCore.DataProtection.DataProtectionCommonExtensions.Protect(IDataProtector protector,String plaintext)
at Microsoft.Azure.WebJobs.Script.WebHost.DataProtectionKeyValueConverter.WriteValue(Key key) at C:\azure-webjobs-sdk-script\src\WebJobs.Script.WebHost\Security\DataProtectionKeyValueConverter.cs : 60
at Microsoft.Azure.WebJobs.Script.WebHost.SecretManager.GenerateHostSecrets() at C:\azure-webjobs-sdk-script\src\WebJobs.Script.WebHost\Security\SecretManager.cs : 357
at async Microsoft.Azure.WebJobs.Script.WebHost.SecretManager.GetHostSecretsAsync() at C:\azure-webjobs-sdk-script\src\WebJobs.Script.WebHost\Security\SecretManager.cs : 76
at async Microsoft.Azure.WebJobs.Script.WebHost.WebJobsSdkExtensionHookProvider.GetOrCreateExtensionKey(String extensionName) at C:\azure-webjobs-sdk-script\src\WebJobs.Script.WebHost\WebHooks\WebJobsSdkExtensionHookProvider.cs : 71
at Microsoft.Azure.WebJobs.Script.WebHost.WebJobsSdkExtensionHookProvider.GetExtensionWebHookRoute(String extensionName) at C:\azure-webjobs-sdk-script\src\WebJobs.Script.WebHost\WebHooks\WebJobsSdkExtensionHookProvider.cs : 64
at Microsoft.Azure.WebJobs.Script.WebHost.WebJobsSdkExtensionHookProvider.GetUrl(IExtensionConfigProvider extension) at C:\azure-webjobs-sdk-script\src\WebJobs.Script.WebHost\WebHooks\WebJobsSdkExtensionHookProvider.cs : 49
at Microsoft.Azure.WebJobs.Host.Config.ExtensionConfigContext.GetWebhookHandler()
at Microsoft.Azure.WebJobs.Extensions.EventGrid.EventGridExtensionConfig.Initialize(ExtensionConfigContext context)
at Microsoft.Azure.WebJobs.Host.Executors.JobHostConfigurationExtensions.InvokeExtensionConfigProviders(ExtensionConfigContext context)
at Microsoft.Azure.WebJobs.Host.Executors.JobHostConfigurationExtensions.CreateStaticServices(JobHostConfiguration config)
at Microsoft.Azure.WebJobs.JobHost.PopulateStaticServices()
at Microsoft.Azure.WebJobs.Script.Utility.CreateMetadataProvider(JobHost host) at C:\azure-webjobs-sdk-script\src\WebJobs.Script\Utility.cs : 362
at Microsoft.Azure.WebJobs.Script.ScriptHost.LoadCustomExtensions() at C:\azure-webjobs-sdk-script\src\WebJobs.Script\Host\ScriptHost.cs : 673
at Microsoft.Azure.WebJobs.Script.ScriptHost.Initialize() at C:\azure-webjobs-sdk-script\src\WebJobs.Script\Host\ScriptHost.cs : 507
at Microsoft.Azure.WebJobs.Script.ScriptHost.Create(IScriptHostEnvironment environment,IScriptEventManager eventManager,ScriptHostConfiguration scriptConfig,ScriptSettingsManager settingsManager) at C:\azure-webjobs-sdk-script\src\WebJobs.Script\Host\ScriptHost.cs : 937
```

In wawsTest:

FunctionsLogs
| where PreciseTimeStamp > datetime(2017-08-29 17:49:29.4963218)
| where PreciseTimeStamp < datetime(2017-08-29 19:47:22.4425563)
| where Tenant == "997fd14cb6b94f5e9b73618c8624efdc"
| where AppName != "functionswarmupsite"

Start with Security/DataProtectionKeyValueConverter.cs at the reported line, then trace SecretManager.GenerateHostSecrets and WebJobsSdkExtensionHookProvider during private deployment startup. Reproduce the failure in the reported wawsTest context and determine why the key ring has no valid default protection key; done means extension initialization no longer throws the reported CryptographicException.

Written by the indexing model from the issue text.