External Account API: initial SEP draft

[antb123]

Summary

Submits the External Account API draft for inclusion as a SEP. The draft
defines a standard API for wallets and clients to request provisioned inbound
receiving instruments (crypto deposit addresses, virtual bank accounts, bank
account credentials) bound to an authenticated Stellar wallet, with SEP-10 /
SEP-45 authentication.

This proposal has been iterated in discussion #1902
since 2026-03-19.

The submitted filename follows the README convention: sep_externalaccount.md.
The preamble currently claims SEP: 0058 — maintainers are welcome to assign
whatever number is appropriate.

SEP-58 number conflict — for maintainer attention

The preamble requests SEP-58. I am aware that #1933 assigned SEP-0058 to
@leighmcculloch's Contract Build Reproducibility draft. The two drafts
overlap in number only — they cover different problem spaces.

Timeline:

• SEP-0058: External Account API — Provisioned Receiving Instruments for Stellar Wallets #1902 (this draft, External Account API): opened 2026-03-19, iterated to v0.3.0 in public discussion.
• Contract Source Verification using Docker without Attestation #1923 (Contract Build Reproducibility): opened 2026-05-01, PR SEP-0058: Contract build reproducibility #1933 merged 2026-05-09 assigning SEP-58.

I am coordinating with @leighmcculloch out of band. I'm happy to take any
SEP number maintainers think fits — this submission flags the timing for
the record; please assign whatever works. The substantive ask is for the
draft itself to be accepted into the repo.

v0.4.0 highlights

• Adds currency to crypto_address offerings, requests, and account
  responses to disambiguate multi-currency-per-chain offerings (motivated by
  real anchor deployments — e.g. Bridge offering both USDC and USDT on
  eip155:1).
• Updates the crypto_address idempotency key to
  (authenticated_subject, kind, chain_id, currency).
• Adds a Future Work section flagging deferred SEP-45 / CAP-67 refinements
  and a possible message field on the KYC 403 body.

Test plan

• Maintainer review of preamble and filename
• Maintainer assigns SEP number (renames file to sep-XXXX.md at merge)
• Markdown lint / prettier passes on the ecosystem folder
• Discussion thread SEP-0058: External Account API — Provisioned Receiving Instruments for Stellar Wallets #1902 linked from the assigned SEP for context

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds a new draft SEP-58 specification defining an “External Account API” for provisioning reusable inbound receiving instruments (crypto deposit addresses, virtual bank accounts, bank credentials) bound to an authenticated Stellar account.

Changes:

• Introduces SEP-58 with discovery, authentication (SEP-10/SEP-45), and core resource/object model.
• Specifies endpoints (/info, /accounts, /accounts/:id), lifecycle/status semantics, and idempotency rules.
• Defines webhook/callback guidance reusing SEP-6 signing conventions and KYC remediation via SEP-12.

[leighmcculloch]

SEP numbers are assigned by the person merging the changes into the repository. I've assigned SEP-59 to the proposal, and updated the self-references within to match, and formatted the file.

Recommend avoiding self-references and within a proposal instead saying "This proposal" as is very common in other SEPs.

GitHub Copilot ran on this PR and made some suggestions that may or may not be of interest in a follow up but that's up to you.

Thanks!