exchange: Add token-2022 info (#42)

* exchange: Add token-2022 info

* Add extension-specific info

docs/more/exchange.md

@@ -804,7 +804,7 @@ accounts do not:
 1. SPL Token accounts must remain
    [rent-exempt](/docs/core/accounts.md#rent-exemption) for the duration of
    their existence and therefore require a small amount of native SOL tokens be
-   deposited at account creation. For SPL Token v2 accounts, this amount is
+   deposited at account creation. For SPL Token accounts, this amount is
    0.00203928 SOL (2,039,280 lamports).
 
 #### Command Line
@@ -915,8 +915,8 @@ via a
 [TransferChecked](https://github.com/solana-labs/solana-program-library/blob/fc0d6a2db79bd6499f04b9be7ead0c400283845e/token/program/src/instruction.rs#L268)
 instruction. Note that it is possible that the ATA address does not yet exist,
 at which point the exchange should fund the account on behalf of the user. For
-SPL Token v2 accounts, funding the withdrawal account will require 0.00203928
-SOL (2,039,280 lamports).
+SPL Token accounts, funding the withdrawal account will require 0.00203928 SOL
+(2,039,280 lamports).
 
 Template `spl-token transfer` command for a withdrawal:
 
@@ -936,6 +936,159 @@ account at will, rendering the account unusable until thawed. If this feature is
 in use, the freeze authority's pubkey will be registered in the SPL Token's mint
 account.
 
+### Basic Support for the SPL Token-2022 (Token-Extensions) Standard
+
+[SPL Token-2022](https://spl.solana.com/token-2022) is the newest standard for
+wrapped/synthetic token creation and exchange on the Solana blockchain.
+
+Also known as "Token Extensions", the standard contains many new features that
+token creators and account holders may optionally enable. These features include
+confidential transfers, fees on transfer, closing mints, metadata, permanent
+delegates, immutable ownership, and much more. Please see the
+[extension guide](https://spl.solana.com/token-2022/extensions) for more
+information.
+
+If your exchange supports SPL Token, there isn't a lot more work required to
+support SPL Token-2022:
+
+- the CLI tool works seamlessly with both programs starting with version 3.0.0.
+- `preTokenBalances` and `postTokenBalances` include SPL Token-2022 balances
+- RPC indexes SPL Token-2022 accounts, but they must be queried separately with
+  program id `TokenzQdBNbLqP5VEhdkAS6EPFLC1PHnBqCXEpPxuEb`
+
+The Associated Token Account works the same way, and properly calculates the
+required deposit amount of SOL for the new account.
+
+Because of extensions, however, accounts may be larger than 165 bytes, so they
+may require more than 0.00203928 SOL to fund.
+
+For example, the Associated Token Account program always includes the "immutable
+owner" extension, so accounts take a minimum of 170 bytes, which requires
+0.00207408 SOL.
+
+### Extension-Specific Considerations
+
+The previous section outlines the most basic support for SPL Token-2022. Since
+the extensions modify the behavior of tokens, exchanges may need to change how
+they handle tokens.
+
+It is possible to see all extensions on a mint or token account:
+
+```bash
+$ spl-token display <account address>
+```
+
+#### Transfer Fee
+
+A token may be configured with a transfer fee, where a portion of transferred
+tokens are withheld at the destination for future collection.
+
+If your exchange transfers these tokens, beware that they may not all arrive at
+the destination due to the withheld amount.
+
+It is possible to specify the expected fee during a transfer to avoid any
+surprises:
+
+```bash
+$ spl-token transfer --expected-fee <fee amount> --fund-recipient <exchange token account> <withdrawal amount> <withdrawal address>
+```
+
+#### Mint Close Authority
+
+With this extension, a token creator may close a mint, provided the supply of
+tokens is zero.
+
+When a mint is closed, there may still be empty token accounts in existence, and
+they will no longer be associated to a valid mint.
+
+It is safe to simply close these token accounts:
+
+```bash
+$ spl-token close --address <account address>
+```
+
+#### Confidential Transfer
+
+Mints may be configured for confidential transfers, so that token amounts are
+encrypted, but the account owners are still public.
+
+Exchanges may configure token accounts to send and receive confidential
+transfers, to hide user amounts. It is not required to enable confidential
+transfers on token accounts, so exchanges can force users to send tokens
+non-confidentially.
+
+To enable confidential transfers, the account must be configured for it:
+
+```bash
+$ spl-token configure-confidential-transfer-account --address <account address>
+```
+
+And to transfer:
+
+```bash
+$ spl-token transfer --confidential <exchange token account> <withdrawal amount> <withdrawal address>
+```
+
+During a confidential transfer, the `preTokenBalance` and `postTokenBalance`
+fields will show no change. In order to sweep deposit accounts, you must decrypt
+the new balance to withdraw the tokens:
+
+```bash
+$ spl-token apply-pending-balance --address <account address>
+$ spl-token withdraw-confidential-tokens --address <account address> <amount or ALL>
+```
+
+#### Default Account State
+
+Mints may be configured with a default account state, such that all new token
+accounts are frozen by default. These token creators may require users to go
+through a separate process to thaw the account.
+
+#### Non-Transferable
+
+Some tokens are non-transferable, but they may still be burned and the account
+can be closed.
+
+#### Permanent Delegate
+
+Token creators may designate a permanent delegate for all of their tokens. The
+permanent delegate may transfer or burn tokens from any account, potentially
+stealing funds.
+
+This is a legal requirement for stablecoins in certain jurisdictions, or could
+be used for token repossession schemes.
+
+Beware that these tokens may be transferred without your exchange's knowledge.
+
+#### Transfer Hook
+
+Tokens may be configured with an additional program that must be called during
+tranfers, in order to validate the transfer or perform any other logic.
+
+Since the Solana runtime requires all accounts to be explicitly passed to a
+program, and transfer hooks require additional accounts, the exchange needs to
+create transfer instructions differently for these tokens.
+
+The CLI and instruction creators such as
+`createTransferCheckedWithTransferHookInstruction` add the extra accounts
+automatically, but the additional accounts may also be specified explicitly:
+
+```bash
+$ spl-token transfer --transfer-hook-account <pubkey:role> --transfer-hook-account <pubkey:role> ...
+```
+
+#### Required Memo on Transfer
+
+Users may configure their token accounts to require a memo on transfer.
+
+Exchanges may need to prepend a memo instruction before transferring tokens back
+to users, or they may require users to prepend a memo instruction before sending
+to the exchange:
+
+```bash
+$ spl-token transfer --with-memo <memo text> <exchange token account> <withdrawal amount> <withdrawal address>
+```
+
 ## Testing the Integration
 
 Be sure to test your complete workflow on Solana devnet and testnet