Portal

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Portal
Introduction
Portal feature can be used to allow supplied assets to seamlessly flow between Aave markets on different networks.
This feature can be used by bridging protocol. There are no core-protocol methods for end-user to take advantage of Portals directly.
Aave protocol V3 allows approved bridges to burn aTokens on the source network while instantly minting them on the destination network. The underlying assets can then be supplied to Aave on the destination network, in a deferred manner, by passing it to the pool after it has been moved through a bridge.
How it works?
Consider a scenario where a user wants to move funds from Ethereum to an L2 or another chain (eg., Arbitrum, Avalanche):
The user submit bridge tx to verified bridging protocol (say Connext) and have access to funds on the destination chain as soon as tx is mined.
Behind the scenes, bridging protocol:
mints unbacked aTokens, on the destination chain, to the intermediate contract and in-turn withdraw and transfer underlying asset to the user immediately.
batch multiple bridge tx and actually move the underlying asset to L2
Later once the funds are available on L2, bridge contract on L2 (i.e. with BRIDGE permissions on Aave V3) supply the underlying asset and fee to the Aave pool to back the previously minted unbacked aTokens.
There are 3 parts involved in taking advantage of this feature:
Approve contracts for BRIDGE role
function addBridge (bridge)
Since, only the contracts (addresses) added to the list of BRIDGE role members can move the supplied liquidity across Aave V3 markets, the Aave Governance must have granted the required permissions/role to the verified Bridge Contract via ACLManager.
The interest rate computation is part of the core protocol but the calculation of the deferred supplies to cover unbacked amount and protocol fee is not enforced by the core protocol. Hence, caution must be taken by governance while approving the bridges.
Have access to liquidity on destination network instantly
function mintUnbacked (asset, amount, onBehalfOf, referralCode)
The contracts with BRIDGE role can access supplied assets in Aave V3 across network instantly by calling mintUnbacked in Pool.sol. The address specified by onBehalfOf will have access to the respective amount of aToken.
To prevent potential risks of excessive minting of unbacked aTokens, an unbackedMintCap is specified per asset.
Back the liquidity after moving funds through bridge
function backUnbacked (asset, amount, fee)
Once the underlying asset are moved to the destination network via Cross Chain Bridge, it can be supplied to Aave V3 pool on the destination network along with the fee by calling backUnbacked in Pool.sol.
The amount to back and fee paid to the protocol is decided by the governance vote for BRIDGE role.
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