Pause and Unpause the Bridge

# Why do it?

The OptimismPortal is a bridge contract that makes it possible to send messages between your L1 and your L2 OP Stack chain. The OptimismPortal is pausable as a backup safety mechanism that allows a specific GUARDIAN address to temporarily halt deposits and withdrawals to mitigate security issues if necessary. An OP Stack chain does not have to specify a usable GUARDIAN address if it does not want to make the OptimismPortal contract pausable, it can specify an address such as zero.

# Who can do it?

OptimismPortal (opens new window) has an immutable GUARDIAN. That address can call pause (opens new window) and unpause (opens new window).

# Changing the guardian

The guardian created by the setup script is the admin account. This is sufficient for testing, but for a production system you would want the guardian to be a multisig with trusted security council.

The GUARDIAN variable is immutable, but the OptimismPortal contract sits behind a proxy, so the GUARDIAN can be modified by changing the OptimismPortal proxy to point to a new implementation contract. You do this using the L1 ProxyAdmin (opens new window) contract.