Delegation fails in older Chrome browsers without Ed25519 support

[burdiyan]

Problem

The delegation protocol requires Ed25519 cryptography to create and sign session keys in the browser via WebCrypto. Older Chrome browsers (pre-v91) do not support Ed25519, causing delegation flows to fail when users attempt to sign in with Hypermedia identity.

Context

Per @vault/docs/delegation.md, the delegation ceremony depends on:

• Creating a non-extractable session key in WebCrypto
• Generating a signature proof over the request payload
• Validating signatures on the callback

These operations currently assume Ed25519 availability but fail silently or with cryptic errors on browsers lacking this algorithm.

Impact

Users on older Chrome versions cannot use the delegation flow, breaking the "Sign in with Hypermedia" experience for them.

Solution needed

• Investigate fallback algorithms or polyfills for older browsers
• Implement graceful error handling/user messaging when Ed25519 is unavailable
• Consider browser support matrix and feasibility of supporting pre-v91 Chrome
• Test delegation flow on affected browser versions

[GaboHBeaumont]

FWIW. I have updated my chrome iOS app to the latest and I still have the issue.