`hermes mcp login <server> --flow device` took `authorization_servers[0]`
from the protected-resource metadata and failed when that entry was a
browser-only or issuer-inconsistent server, even though a later entry was
the issuer-bound device_code server meant for headless clients (Higgsfield
advertises exactly this shape: a PKCE server first, the device server second).
Discovery now tries each advertised server in order and binds to the first
whose metadata issuer matches its advertised URL and that offers device
authorization. Issuer validation (RFC 8414 / SEP-2468) is unchanged per
server; a single-server resource raises exactly the error it raised before,
and a multi-server resource with no usable entry reports every attempt.
The browser path (`tools/mcp_oauth_manager.py` pre-flight) is deliberately
left on the SDK's own first-entry selection: the SDK's 401-branch discovery
re-selects `authorization_servers[0]` itself, so a divergent pre-flight pick
would only desynchronise the cached metadata from what the SDK authorizes against.
Add explicit RFC 8628 device login and oauth.flow selection while keeping
browser PKCE and the SDK runtime refresh path. Reuse issuer/resource
validation, configured client authentication and profile-scoped storage.
Only persist an approved, validated grant; never echo endpoint error bodies.
Slim redo of #104752 by @wjorgensen, replacing duplicate HTTP/storage
wrappers with the existing SDK and two real-wire invariant tests.
Refs #104742
Co-authored-by: Wes Hermes <weshermes@Wess-Mac-mini.localdomain>
teknium1