MYSO-28: Quoting policy manager

[asardon]

Description

When delegating quoting to an on-chain quoting delegate (see #583) or a set of off-chain quote signers then vault owners don't have any control over what kind of quotes are being submitted. This creates significant friction when wanting to delegate quoting to 3rd parties in a trust-minimized way.

Recommendation

Add a quote policy manager in which vault owners can define rules according to which quotes that get produced by on-chain quote delegates and/or off-chain quote signers are processed.

Use Cases

Use Case 1:

• Mantle treasury wants to lend USDC against $MNT
• Treasury wants to delegate quoting to MYSO (either as on-chain quote delegate or as off-chain quote signer)
• Treasury wants to ensure that we quote only within tenor of 1-6m, LTV between 10-70% and APR>0
• Moreover, treasury wants to ensure that we only quote for USDC/$MNT and nothing else
  => requirements: (1) only allow certain pairs and block all others, (2) apply tenor, LTV and APR policy to given pair

Use Case 2:

• Solo lender wants to lend USDC against $WETH, $wBTC, $RPL, $rETH
• Solo lender wants to quote off-chain to produce large number of quotes across whole LTV/tenor matrix at low cost
• To streamline the process, solo lender sets 1 hot wallet as signer for easier off-chain quoting
• For greater peace of mind, solo lender wants to add a policy ensuring that all quotes are within 1-6m tenor, LTV is between 10-70% (if oracle exists), and APR is always >0
  => requirements: (1) ensure that all quotes adhere to global policy, (2) ensure only quotes with oracles go through and (3) for all quotes without oracle, ie RPL, allow to overwrite an explicit loan-per-collateral unit range

Use Case 3:

• Solo lender wants to lend USDC against $WETH
• Solo lender wants to quote off-chain to produce large number of quotes across whole LTV/tenor matrix at low cost
• To streamline the process, solo lender sets 1 hot wallet as signer for easier off-chain quoting
• In parallel, solo lender also wants to lend USDC against more experimental collateral types from time to time
• For this, solo lender wants to also use off-chain quoting but impose a higher signer threshold
  => requirements: (1) allow for different off-chain signer threshold overwrites, (2) allow quoting on all pairs without having to whitelist beforehand

[asardon]

Implementation

An optional quote policy manager has been integrated into the _checkSenderAndPolicyAndQuoteInfo method and is called on every borrow (ie both with on- and off-chain quotes), ie for on-chain quotes here:

v2/contracts/peer-to-peer/QuoteHandler.sol

Lines 167 to 173 in 93bf122

	// @dev: ignore returned minNumOfSignersOverwrite for on-chain quotes
	_checkSenderAndPolicyAndQuoteInfo(
	borrower,
	lenderVault,
	onChainQuote.generalQuoteInfo,
	onChainQuote.quoteTuples[quoteTupleIdx]
	);

and for off-chain quotes here:

v2/contracts/peer-to-peer/QuoteHandler.sol

Lines 200 to 205 in 93bf122

	uint256 minNumOfSignersOverwrite = _checkSenderAndPolicyAndQuoteInfo(
	borrower,
	lenderVault,
	offChainQuote.generalQuoteInfo,
	quoteTuple
	);

Note that in the case of off-chain quotes we allow the vault owner to overwrite their own min signer threshold via minNumOfSignersOverwrite. This allows the vault owner to set a higher default min signer threshold and only lower it eg for bluechips where tighter policy bounds can be set while having a higher signer threshold for all other and potentially more risky cases.

The quote policy manager itself is a peripheral contract that can be whitelisted to the address registry and where additional implementations can also be added later on. A basic policy manager is implemented here:

v2/contracts/peer-to-peer/policyManagers/BasicQuotePolicyManager.sol

Line 15 in 93bf122

contract BasicQuotePolicyManager is IQuotePolicyManager {

Note that in the policy manager there are two types of policies each lender vault owner can set, ie global policies that apply on a global level across all quotes as well as pair policies that only apply for a specific collateral/loan token pair. Moreover, note that the pair policies always take precedence over the global policy.