eBTC Rate Provider

Fixes #134

rate-providers/eBTCRateProvider.md

@@ -0,0 +1,50 @@
+# Rate Provider: `eBtcRateProvider`
+
+## Details
+- Reviewed by: @mkflow27
+- Checked by: @\<GitHub handle of secondary reviewer\>
+- Deployed at:
+    - [ethereum:0x81Be3526A71D9013A1a5bD38758e0f248231b523](https://etherscan.io/address/0x81be3526a71d9013a1a5bd38758e0f248231b523#code)
+- Audit report(s):
+    - [Protocol audits](https://github.com/Se7en-Seas/boring-vault/tree/main/audit)
+
+## Context
+eBTC is a Bitcoin-backed liquidty restaking token. eBTC is backed by LBTC. The staking portion of eBTC is done by Babylon. For more information see the [eBTC documentation](https://etherfi.gitbook.io/etherfi/lrts/ebtc-bitcoin-lrt). 
+
+## Review Checklist: Bare Minimum Compatibility
+Each of the items below represents an absolute requirement for the Rate Provider. If any of these is unchecked, the Rate Provider is unfit to use.
+
+- [x] Implements the [`IRateProvider`](https://github.com/balancer/balancer-v2-monorepo/blob/bc3b3fee6e13e01d2efe610ed8118fdb74dfc1f2/pkg/interfaces/contracts/pool-utils/IRateProvider.sol) interface.
+- [x] `getRate` returns an 18-decimal fixed point number (i.e., 1 == 1e18) regardless of underlying token decimals.
+
+## Review Checklist: Common Findings
+Each of the items below represents a common red flag found in Rate Provider contracts.
+
+If none of these is checked, then this might be a pretty great Rate Provider! If any of these is checked, we must thoroughly elaborate on the conditions that lead to the potential issue. Decision points are not binary; a Rate Provider can be safe despite these boxes being checked. A check simply indicates that thorough vetting is required in a specific area, and this vetting should be used to inform a holistic analysis of the Rate Provider.
+
+### Administrative Privileges
+- [x] The Rate Provider is upgradeable (e.g., via a proxy architecture or an `onlyOwner` function that updates the price source address).
+
+- [ ] Some other portion of the price pipeline is upgradeable (e.g., the token itself, an oracle, or some piece of a larger system that tracks the price).
+### Oracles
+- [x] Price data is provided by an off-chain source (e.g., a Chainlink oracle, a multisig, or a network of nodes). 
+    - source: tbd.
+    - source address: not set
+    - any protections? NO
+    - comment: The rate provider reads a state variable in the `AccountantWithRateProvider` contract [ethereum:0x1b293DC39F94157fA0D1D36d7e0090C8B8B8c13F](https://etherscan.io/address/0x1b293DC39F94157fA0D1D36d7e0090C8B8B8c13F#code). This state variable can by upgraded by authorized parties calling `updateExchangeRate(uint96 newExchangeRate)`, making the authorized parties the effective price oracles. Authorization is managed by assigning roles the right to call a particular function. This is managed by the `authority` contract deployed at [ethereum:0x6889E57BcA038C28520C0B047a75e567502ea5F6](https://etherscan.io/address/0x6889E57BcA038C28520C0B047a75e567502ea5F6#code). By inspecting [this](https://etherscan.io/tx/0xb21d447fbaa73159d20cc2ecc508e224cdd66e41378601001af09308f3df16c0) transaction, the right to call `updateExchangeRate` has been assigned to role 11. However upon inspection of all `UserRoleUpdated(address indexed user, uint8 indexed role, bool enabled)` events it turns out that currently no account is authorized to set the rate. Leading to the assumption that this will be done in a time after this review.
+
+    Assuming this is the case in the future only the `owner` of the `authority` contract can assign new roles to users by calling `setUserRole` on the `authority` contract. This right currently lives within a gnosis safe multisig (4/6). 
+
+
+- [ ] Price data is expected to be volatile (e.g., because it represents an open market price instead of a (mostly) monotonically increasing price).
+
+### Common Manipulation Vectors
+- [ ] The Rate Provider is susceptible to donation attacks.
+
+## Additional Findings
+To save time, we do not bother pointing out low-severity/informational issues or gas optimizations (unless the gas usage is particularly egregious). Instead, we focus only on high- and medium-severity findings which materially impact the contract's functionality and could harm users.
+
+## Conclusion
+**Summary judgment: \<SAFE/UNSAFE\>**
+
+This rate provider should work well with Balancer pools assuming that no wrong rates get pushed. The preferred option would be for the rate Provider to use `getRateSafe` of the `AccountantWithRateProviders` to ensure the transaction on Balancer reverts if the underlying system has been paused due to a above threshold price being pushed as part of a oracle price update transaction.

rate-providers/registry.json

@@ -1358,6 +1358,15 @@
           "implementationReviewed": "0x0b75F2B048CA8517f6476316F872903920DCC8ef"
         }
       ]
+    },
+    "0x81Be3526A71D9013A1a5bD38758e0f248231b523": {
+      "asset": "0x657e8C867D8B37dCC18fA4Caead9C45EB088C642",
+      "name": "eBtcRateProvider",
+      "summary": "",
+      "review": "./eBTCRateProvider.md",
+      "warnings": [""],
+      "factory": "",
+      "upgradeableComponents": []
     }
   },
   "fantom": {