L2 to L2 native token bridge (with mapping)

[dpbpolymer]

User story:

• As a rollup I want to help users bridge existing tokens from other chains to improve liquidity and prevent unnecessary wrapped tokens on my chain.

Objectives:

• Primary objective: Build a lock and mint bridge with a feature to whitelist L2 and give them minting rights of the token contracts.
• Secondary objective: Build an L2 to L2 token mapping between an existing tokens on a L2 and deploy its corresponding new token contract on a destination L2.

Implementation tips:

• Usually token mapping for a rollup is done between L1 and L2, but given the landscape of rising rollups and liquidity fragmentation it has become important to allow free flow of assets between L2s.
• Polymer is best fit for this task as it uses the native L1<>L2 bridge for settlement when bridging between rollups, thus has the same security as that of the native bridge.
• You need to build a system that deploys a standardized vault for locking tokens on the source, and either mints tokens with the same token ticker on the destination, or mints from an existing contract you provide the rights.
• Note that currently our testnet only supports 2 chains, making this a relatively trivial task. In future a rollup can choose to allow token mapping from another rollup. In that case, you must make sure they mint from the same token contract and not create another representation.

References: Mapping tokens from L1 to L2