Unique Usernames in Identity Pallet (#2651)

This PR allows _username authorities_ to issue unique usernames that
correspond with an account. It also provides two-way lookup, that is
from `AccountId` to a single, "primary" `Username` (alongside
`Registration`) and multiple unique `Username`s to an `AccountId`.

Key features:

- Username Authorities added (and removed) via privileged origin.
- Authorities have a `suffix` and an `allocation`. They can grant up to
`allocation` usernames. Their `suffix` will be appended to the usernames
that they issue. A suffix may be up to 7 characters long.
- Users can ask an authority to grant them a username. This will take
the form `myusername.suffix`. The entire name (including suffix) must be
less than or equal to 32 alphanumeric characters.
- Users can approve a username for themselves in one of two ways (that
is, authorities cannot grant them arbitrarily):
- Pre-sign the entire username (including suffix) with a secret key that
corresponds to their `AccountId` (for keyed accounts, obviously); or
- Accept the username after it has been granted by an authority (it will
be queued until accepted) (for non-keyed accounts like pure proxies or
multisigs).
- The system does not require any funds or deposits. Users without an
identity will be given a default one (presumably all fields set to
`None`). If they update this info, they will need to place the normal
storage deposit.
- If a user does not have any username, their first one will be set as
`Primary`, and their `AccountId` will map to that one. If they get
subsequent usernames, they can choose which one to be their primary via
`set_primary_username`.
- There are some state cleanup functions to remove expired usernames
that have not been accepted and dangling usernames whose owners have
called `clear_identity`.

TODO:

- [x] Add migration to runtimes
- [x] Probably do off-chain migration into People Chain genesis
- [x] Address a few TODO questions in code (please review)

---------

Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>
Co-authored-by: Gonçalo Pestana <g6pestana@gmail.com>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Dónal Murray <donal.murray@parity.io>

cumulus/parachains/runtimes/people/people-westend/src/people.rs

@@ -22,9 +22,12 @@ use frame_support::{
 	RuntimeDebugNoBound,
 };
 use pallet_identity::{Data, IdentityInformationProvider};
-use parachains_common::impls::ToParentTreasury;
+use parachains_common::{impls::ToParentTreasury, DAYS};
 use scale_info::TypeInfo;
-use sp_runtime::{traits::AccountIdConversion, RuntimeDebug};
+use sp_runtime::{
+	traits::{AccountIdConversion, Verify},
+	RuntimeDebug,
+};
 use sp_std::prelude::*;
 
 parameter_types! {
@@ -51,6 +54,12 @@ impl pallet_identity::Config for Runtime {
 	type Slashed = ToParentTreasury<RelayTreasuryAccount, LocationToAccountId, Runtime>;
 	type ForceOrigin = EnsureRoot<Self::AccountId>;
 	type RegistrarOrigin = EnsureRoot<Self::AccountId>;
+	type OffchainSignature = Signature;
+	type SigningPublicKey = <Signature as Verify>::Signer;
+	type UsernameAuthorityOrigin = EnsureRoot<Self::AccountId>;
+	type PendingUsernameExpiration = ConstU32<{ 7 * DAYS }>;
+	type MaxSuffixLength = ConstU32<7>;
+	type MaxUsernameLength = ConstU32<32>;
 	type WeightInfo = weights::pallet_identity::WeightInfo<Runtime>;
 }
 
@@ -84,7 +93,6 @@ pub enum IdentityField {
 	TypeInfo,
 )]
 #[codec(mel_bound())]
-#[cfg_attr(test, derive(frame_support::DefaultNoBound))]
 pub struct IdentityInfo {
 	/// A reasonable display name for the controller of the account. This should be whatever it is
 	/// that it is typically known as and should not be confusable with other entities, given
@@ -202,3 +210,21 @@ impl IdentityInfo {
 		res
 	}
 }
+
+/// A `Default` identity. This is given to users who get a username but have not set an identity.
+impl Default for IdentityInfo {
+	fn default() -> Self {
+		IdentityInfo {
+			display: Data::None,
+			legal: Data::None,
+			web: Data::None,
+			matrix: Data::None,
+			email: Data::None,
+			pgp_fingerprint: None,
+			image: Data::None,
+			twitter: Data::None,
+			github: Data::None,
+			discord: Data::None,
+		}
+	}
+}