feat(saml): wire SAML 2.0 SSO end-to-end (pure-Rust) + Settings/Storage UI consolidation (v0.5.1)

SAML SSO (the config was storage-only since v0.4.5; now it logs you in):
- New openpxe-core::saml — pure-Rust SP built on bergshamra (XML-DSig +
  exclusive c14n via RustCrypto, no OpenSSL/xmlsec/libxml2). The static
  musl binary stays C-free; samael was rejected for hard-requiring OpenSSL.
  * metadata.rs   — parse IdP EntityDescriptor (SSO URLs + signing certs),
                    build our SP metadata.
  * authn_request.rs — build + HTTP-Redirect-encode AuthnRequests.
  * response.rs   — verify the signature against the pinned IdP cert
                    (trusted_keys_only + strict_verification for XSW),
                    then enforce Status/Destination/Audience/time-bounds/
                    signature-scope. Stateless; returns the IDs the HTTP
                    layer needs.
- http-api saml_routes: GET /api/sso/login (302 to IdP), POST /api/sso/acs
  (verify -> InResponseTo correlation / IdP-initiated gating / assertion
  replay guard -> mint operator session -> 302), GET /api/sso/metadata.
  Added to the pre-auth allowlist; /api/sso config stays gated.
- SsoConfig gains entity_id (SP Entity ID, defaults to public base URL)
  and allow_idp_initiated (default off), mirroring FleetDM.
- Access model: any IdP-authenticated, cryptographically-verified user gets
  an operator session (single-tier; local admin remains the fallback owner).
- Login page: the "Sign in with <IdP>" button now drives the real flow and
  surfaces sso_error redirects.

UI consolidation:
- Removed the Advanced sidebar tab; folded its webhook-notifications +
  API-reference cards into a collapsible "Advanced" disclosure at the
  bottom of Settings.
- Merged the Storage tab's separate SMB and NFS cards into one "Remote
  shares" card with a protocol dropdown and a unified, protocol-badged
  table. No backend changes — same /api/smb-shares + /api/nfs-shares.

Tests: 17 SAML core tests (accept + reject tampered/unsigned/wrong-key/
wrong-audience/expired/future/wrong-issuer/non-success) and 6 ACS
integration tests (happy path, IdP-initiated gating, SP correlation,
replay, garbage). Full workspace: 206 tests green, clippy clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

crates/core/src/saml/mod.rs

@@ -0,0 +1,92 @@
+//! Pure-Rust SAML 2.0 Service Provider (v0.5.1).
+//!
+//! This module implements the SP half of a SAML Web-Browser-SSO profile:
+//!
+//! * [`metadata`] — parse the IdP's `EntityDescriptor` (SSO URLs + signing
+//!   certificates) and build *our* SP metadata for the IdP admin to import.
+//! * [`authn_request`] — build an `AuthnRequest` and encode it for the
+//!   HTTP-Redirect binding.
+//! * [`response`] — decode a `SAMLResponse`, **verify its XML signature**
+//!   against the IdP's pinned certificate (via the pure-Rust `bergshamra`
+//!   crate — no OpenSSL/libxml2/xmlsec, so the static musl binary stays
+//!   C-free), then enforce the SP-side semantic checks (Status, Destination,
+//!   Audience, time bounds) that are where SAML SPs actually get attacked.
+//!
+//! Stateful checks (replay of assertion IDs, correlating `InResponseTo`
+//! against requests *we* issued, gating IdP-initiated login) live in the
+//! HTTP layer — [`response::consume`] is deliberately stateless and returns
+//! the IDs the caller needs to perform them.
+//!
+//! Access model: any assertion the IdP authenticates and we cryptographically
+//! verify yields an operator [`VerifiedPrincipal`]. OpenPXE is single-tier —
+//! there is no per-user role table — and the local admin account remains a
+//! guaranteed fallback owner regardless of SSO state.
+
+pub mod authn_request;
+pub mod metadata;
+pub mod response;
+
+pub use authn_request::AuthnRequest;
+pub use metadata::IdpMetadata;
+pub use response::{VerifiedPrincipal, VerifiedResponse};
+
+use thiserror::Error;
+
+/// Default clock-skew tolerance applied to assertion time bounds. SAML IdPs
+/// and SPs rarely have perfectly synced clocks; 60s matches common practice
+/// (Shibboleth/FleetDM defaults are in this ballpark).
+pub const DEFAULT_CLOCK_SKEW_SECS: i64 = 60;
+
+/// Runtime SP parameters, derived from [`crate::SsoConfig`] + the advertised
+/// public base URL by the HTTP layer.
+#[derive(Debug, Clone)]
+pub struct SpParams {
+    /// Our SP Entity ID (the `<Issuer>` we send and the `Audience` we require
+    /// in responses). Defaults to the public base URL when the operator left
+    /// the Entity ID field blank.
+    pub entity_id: String,
+    /// The Assertion Consumer Service URL the IdP POSTs the response to —
+    /// `<public_base_url>/api/sso/acs`.
+    pub acs_url: String,
+}
+
+/// Everything that can go wrong consuming a SAML response. Kept coarse on
+/// purpose: the HTTP layer logs the detail and shows the operator a generic
+/// "SSO sign-in failed" — we never leak which specific check tripped to the
+/// browser, since that aids an attacker probing the SP.
+#[derive(Debug, Error)]
+pub enum SamlError {
+    #[error("SAML XML parse error: {0}")]
+    Xml(String),
+    #[error("IdP metadata is missing a required element: {0}")]
+    Metadata(String),
+    #[error("no usable IdP signing certificate in metadata")]
+    NoSigningCert,
+    #[error("signature verification failed: {0}")]
+    Signature(String),
+    #[error("the signature does not cover the assertion we read")]
+    SignatureScope,
+    #[error("SAML response status was not Success: {0}")]
+    Status(String),
+    #[error("response is missing a required element: {0}")]
+    MissingElement(String),
+    #[error("encrypted assertions are not supported in this release")]
+    EncryptedAssertionUnsupported,
+    #[error("expected exactly one assertion, found {0}")]
+    AssertionCount(usize),
+    #[error("issuer mismatch: response was not issued by the configured IdP")]
+    IssuerMismatch,
+    #[error("audience mismatch: assertion is not addressed to this service provider")]
+    AudienceMismatch,
+    #[error("response destination does not match our ACS URL")]
+    DestinationMismatch,
+    #[error("assertion is expired or not yet valid")]
+    TimeBounds,
+    #[error("invalid SAML timestamp: {0}")]
+    Timestamp(String),
+    #[error("base64 decode failed: {0}")]
+    Base64(String),
+}
+
+#[cfg(test)]
+mod tests;