Add new extension `WithdrawExcessLamportsAuthority` for mints

[wowinter13]

Recreated from solana-labs/solana-program-library#6858

Problem:
I believe the authority to withdraw excess lamports from a program owned account for SPL 2022 is set with Minth Authority.

Almost all tokens created will revoke the Mint Authority making this a pointless CLI command. I appreciate there are already a lot of authorities but but surely one more can't hurt?

Solution:

• Add a new extension like WithdrawExcessLamportsAuthority just for mints, along with an instruction to initialize the authority
• Add a new WithdrawExcessLamportsAuthority and support it in SetAuthority
• During withdraw_excess_lamports, if the extension exists, then that's the only possible authority that can withdraw lamports, so even the mint authority wouldn't be able to withdraw lamports

FYI: @joncinque

(recreating this one as I plan to implement it this month or next)

[joncinque]

Yep, this makes sense to me, thanks for recreating the issue!

[farajaahdaf]

Real-world use case supporting this feature

I have an active case where 77 SOL was accidentally sent to the BUBBA token mint (BMt3pq4g8ggWWBnd6DJ1jhVyTkHfWjAfJwWW6sRCbQJv) — classic SPL Token Program, mint authority revoked, ~92 SOL currently stranded.

I've exhausted all current options after P-token went live at epoch 971:

• spl-token withdraw-excess-lamports → AuthorityTypeNotSupported (no mint authority, no mint keypair)
• Manual instruction building with all instruction indices → SignatureFailure
• Token-2022 program direct call → same result

The WithdrawExcessLamportsAuthority extension proposed here is exactly the right long-term solution for Token-2022 mints.

For classic Token Program mints, the situation is worse — P-token only allows the mint keypair as fallback authority when mint authority is revoked. If the token creator discarded the mint keypair (common practice), the SOL is permanently lost.

Suggestion: Could the classic token program's P-token upgrade also support a WithdrawExcessLamportsAuthority that can be set retroactively (with appropriate time-lock/governance)? Even a 30-day delay mechanism would be better than permanent loss.

I'm willing to pay a bounty to anyone who can find a recovery path for my specific case. TX: 2qYrJEgBnRDr9h3gTyBKkWjKUdNF4FXQPSfjJkwwaSSKKxpDhudZ5nnhdC4whUR8ZEjBxAFef8KjJQxqDjr7cSsx

This issue matters — there's likely millions of SOL stranded in token mints across the ecosystem. Would love to see this prioritized.

[joncinque]

Sorry, we can't add this functionality to p-token.