Sharepoint: Security Token Service is down or showing errors?

Some examples of errors that may show up in your ULS log.

An exception occurred when trying to issue security token: The server did not provide a meaningful reply; this might be caused by a contract mismatch, a premature session shutdown or an internal server error (OR)
Request for security token failed with exception: System.ServiceModel.ServiceActivationException: The requested service,'http://localhost:32843/SecurityTokenServiceApplication/securitytoken.svc/actas' could not be activated (OR)
An exception occurred when trying to issue security token: The requested service,'http://localhost:32843/SecurityTokenServiceApplication/securitytoken.svc/actas' could not be activated

Run the following commands, it will do a new provisioning of the Security Token Service.

$h = Get-SPServiceHostconfig
$h.Provision()
$services = Get-SPServiceApplication
foreach ($service in $services) { $service.provision();
write-host $service.name}

Perform an IIS Reset and try to browse the STS, http://localhost:32843/SecurityTokenServiceApplication/securitytoken.svc

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