Forms authentication machineKey unable to validate data error in custom security extension

I have followed the guides here to setup a custom security extension. So far the login and ReportServer are working however the Report portal https://localhost/reports has a 500 error. From the logs:

Exception: System.Web.HttpException (0x80004005): Unable to validate data. at System.Web.Configuration.MachineKeySection.EncryptOrDecryptData(Boolean fEncrypt, Byte[] buf, Byte[] modifier, Int32 start, Int32 length, Boolean useValidationSymAlgo, Boolean useLegacyMode, IVType ivType, Boolean signData) at System.Web.Security.FormsAuthentication.Decrypt(String encryptedTicket) at Microsoft.BIServer.Owin.Common.Middleware.CustomAuthenticationMiddleware.CreateRequestContextFromCookie(IOwinContext context) at Microsoft.BIServer.Owin.Common.Middleware.CustomAuthenticationMiddleware.CreatePortalIdentity(IOwinContext context) at Microsoft.BIServer.Owin.Common.Middleware.CustomAuthenticationMiddleware.Invoke(IOwinContext context) at Microsoft.Owin.Security.Infrastructure.AuthenticationMiddleware``1.<Invoke>d__0.MoveNext() --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw() at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task) at Microsoft.BIServer.Owin.Common.Middleware.RequestLoggingMiddleWare.<Invoke>d__2.MoveNext() | RequestID = s_562e4f17-7d98-45e0-b744-02509f01e0d8

Apparently it's having trouble with the machineKey used for encryption.

I have included the machineKey in:

web.config
rsReportServer.config
rsPortal.config

<machineKey validationKey="33A11FDECC5CB917123E44C5BDAF1859942D5FD0D80E1CA3FF2F32576F391556" decryptionKey="1581FF2A206D1A3C283442C84EF2EBD333AE0B27BC85C502E1A771058539C4B1" validation="AES" decryption="AES" />

https://github.com/Microsoft/Reporting-Services/issues/121 Note: I don't mean to duplicate issue 121 which looks the same, it's just that none of the solutions posted there have worked for me.

I've tried many solutions aimed at addressing the machineKey error. Now I found the code for MachineKeySection.cs from Microsoft and it seems the "Unable_To_Validate_Data" error could be masking something else gone wrong.

// It's important that we don't propagate the original exception here as we don't want a production
// server which has unintentionally left YSODs enabled to leak cryptographic information.
            throw new HttpException(SR.GetString(SR.Unable_to_validate_data));

Any suggestions as to what I could be missing?

microsoft / Reporting-Services

Forms authentication machineKey unable to validate data error in custom security extension #252