## Issue Addressed
Closes#2274
## Proposed Changes
* Modify the `YamlConfig` to collect unknown fields into an `extra_fields` map, instead of failing hard.
* Log a debug message if there are extra fields returned to the VC from one of its BNs.
This restores Lighthouse's compatibility with Teku beacon nodes (and therefore Infura)
## Issue Addressed
Closes#1889
## Proposed Changes
- Error when passwords which use invalid UTF-8 characters during encryption.
- Add some tests
## Additional Info
I've decided to error when bad characters are used to create/encrypt a keystore but think we should allow them during decryption since either the keystore was created
- with invalid UTF-8 characters (possibly by another client or someone whose password is random bytes) in which case we'd want them to be able to decrypt their keystore using the right key.
- without invalid characters then the password checksum would almost certainly fail.
Happy to add them to decryption if we want to make the decryption more trigger happy 😋 , it would only be a one line change and would tell the user which character index is causing the issue.
See https://eips.ethereum.org/EIPS/eip-2335#password-requirements
## Issue Addressed
NA
## Proposed Changes
- Implements a HTTP API for the validator client.
- Creates EIP-2335 keystores with an empty `description` field, instead of a missing `description` field. Adds option to set name.
- Be more graceful with setups without any validators (yet)
- Remove an error log when there are no validators.
- Create the `validator` dir if it doesn't exist.
- Allow building a `ValidatorDir` without a withdrawal keystore (required for the API method where we only post a voting keystore).
- Add optional `description` field to `validator_definitions.yml`
## TODO
- [x] Signature header, as per https://github.com/sigp/lighthouse/issues/1269#issuecomment-649879855
- [x] Return validator descriptions
- [x] Return deposit data
- [x] Respect the mnemonic offset
- [x] Check that mnemonic can derive returned keys
- [x] Be strict about non-localhost
- [x] Allow graceful start without any validators (+ create validator dir)
- [x] Docs final pass
- [x] Swap to EIP-2335 description field.
- [x] Fix Zerioze TODO in VC api types.
- [x] Zeroize secp256k1 key
## Endpoints
- [x] `GET /lighthouse/version`
- [x] `GET /lighthouse/health`
- [x] `GET /lighthouse/validators`
- [x] `POST /lighthouse/validators/hd`
- [x] `POST /lighthouse/validators/keystore`
- [x] `PATCH /lighthouse/validators/:validator_pubkey`
- [ ] ~~`POST /lighthouse/validators/:validator_pubkey/exit/:epoch`~~ Future works
## Additional Info
TBC
