Is it permissible to perform Salāh al Jumʿuah in a prison?

If the government does not prohibit doing so and gives permission, it would be permissible to perform Salāh al Jumuʿah in a prison.

The fact that people outside the prison are not allowed to come into the prison to perform Salāh al Jumʿuah will not be taken into consideration as this is due to the general rule of the prison, which is for security reasons.

A ruling similar to this is mentioned in Shāmī (vol. 2 p. 152) with regards to the permissibility of performing of Salāh al Jumuʿah in a closed fort. The door of the fort is closed for security reasons and is not done to stop people outside the fort from coming for Jumuʿah Salāh.

Allah alone knows best