[PATCH proxmox v5 08/27] notify: smtp: add state handling logic

[Arthur Bied-Charreton <a.bied-charreton@proxmox.com>]

Create new state file in add_endpoint, create/update existing one in
update_endpoint and delete it in delete_endpoint.

Add trigger_state_refresh to the Endpoint trait, with no-op default
implementation. Implement it in SmtpEndpoint's Endpoint impl to trigger
an OAuth2 token exchange, in order to rotate an existing token, or
extend its lifetime.

The intended callers are daily update jobs, so on a cluster
`trigger_state_refresh` may be invoked once per node within a
relatively short window. The `last_refreshed` cutoff suppresses
redundant token exchanges.

Signed-off-by: Arthur Bied-Charreton <a.bied-charreton@proxmox.com>
Reviewed-by: Lukas Wagner <l.wagner@proxmox.com>
---
 proxmox-notify/src/api/common.rs     | 19 +++++++
 proxmox-notify/src/api/smtp.rs       | 32 +++++++++++
 proxmox-notify/src/endpoints/smtp.rs | 80 +++++++++++++++++++++++++++-
 proxmox-notify/src/lib.rs            | 28 +++++++++-
 4 files changed, 157 insertions(+), 2 deletions(-)

diff --git a/proxmox-notify/src/api/common.rs b/proxmox-notify/src/api/common.rs
index fa2356e2..220be3de 100644
--- a/proxmox-notify/src/api/common.rs
+++ b/proxmox-notify/src/api/common.rs
@@ -3,6 +3,25 @@ use proxmox_http_error::HttpError;
 use super::http_err;
 use crate::{Bus, Config, Notification};
 
+/// Refresh all notification targets' internal state.
+///
+/// The caller is responsible for any needed permission checks and must hold a lock
+/// on the notifications config. Concurrent updates could otherwise leave the state
+/// files inconsistent with the notifications config (e.g. a stale state file for
+/// an endpoint that was deleted concurrently).
+pub fn trigger_state_refresh(config: &Config) -> Result<(), HttpError> {
+    let bus = Bus::from_config(config).map_err(|err| {
+        http_err!(
+            INTERNAL_SERVER_ERROR,
+            "Could not instantiate notification bus: {err}"
+        )
+    })?;
+
+    bus.trigger_state_refresh();
+
+    Ok(())
+}
+
 /// Send a notification to a given target.
 ///
 /// The caller is responsible for any needed permission checks.
diff --git a/proxmox-notify/src/api/smtp.rs b/proxmox-notify/src/api/smtp.rs
index 0668e89d..24d3d865 100644
--- a/proxmox-notify/src/api/smtp.rs
+++ b/proxmox-notify/src/api/smtp.rs
@@ -116,6 +116,19 @@ pub fn add_endpoint(
 
     let endpoint_config = infer_auth_method(endpoint_config, private_endpoint_config);
 
+    if let Some(token) = oauth2_refresh_token {
+        let oauth_state = State::new(token, proxmox_time::epoch_i64());
+        context()
+            .save_oauth_state(&endpoint_config.name, Some(oauth_state))
+            .map_err(|e| {
+                http_err!(
+                    INTERNAL_SERVER_ERROR,
+                    "could not create state file for '{}': {e}",
+                    &endpoint_config.name
+                )
+            })?;
+    }
+
     config
         .config
         .set_data(&endpoint_config.name, SMTP_TYPENAME, &endpoint_config)
@@ -233,6 +246,18 @@ pub fn update_endpoint(
 
     let endpoint = infer_auth_method(endpoint, get_private_config(config, name)?);
 
+    if let Some(token) = oauth2_refresh_token {
+        let oauth_state = context()
+            .load_oauth_state(name)
+            .map_err(|e| http_err!(INTERNAL_SERVER_ERROR, "{e}"))?
+            .set_oauth2_refresh_token(Some(token))
+            .set_last_refreshed(proxmox_time::epoch_i64());
+
+        context()
+            .save_oauth_state(name, Some(oauth_state))
+            .map_err(|e| http_err!(INTERNAL_SERVER_ERROR, "{e}"))?;
+    }
+
     config
         .config
         .set_data(name, SMTP_TYPENAME, &endpoint)
@@ -305,6 +330,13 @@ pub fn delete_endpoint(config: &mut Config, name: &str) -> Result<(), HttpError>
 
     super::remove_private_config_entry(config, name)?;
 
+    context().save_oauth_state(name, None).map_err(|e| {
+        http_err!(
+            INTERNAL_SERVER_ERROR,
+            "could not delete state for '{name}': {e}"
+        )
+    })?;
+
     config.config.sections.remove(name);
 
     Ok(())
diff --git a/proxmox-notify/src/endpoints/smtp.rs b/proxmox-notify/src/endpoints/smtp.rs
index 74297969..dcc01bb5 100644
--- a/proxmox-notify/src/endpoints/smtp.rs
+++ b/proxmox-notify/src/endpoints/smtp.rs
@@ -1,11 +1,13 @@
 use std::borrow::Cow;
-use std::time::Duration;
+use std::time::{Duration, SystemTime, UNIX_EPOCH};
 
 use lettre::message::header::{HeaderName, HeaderValue};
 use lettre::message::{Mailbox, MultiPart, SinglePart};
 use lettre::transport::smtp::client::{Tls, TlsParameters};
 use lettre::{message::header::ContentType, Message, SmtpTransport, Transport};
+use oauth2::{ClientId, ClientSecret, RefreshToken};
 use serde::{Deserialize, Serialize};
+use tracing::info;
 
 use proxmox_schema::api_types::COMMENT_SCHEMA;
 use proxmox_schema::{api, Updater};
@@ -22,6 +24,7 @@ const SMTP_PORT: u16 = 25;
 const SMTP_SUBMISSION_STARTTLS_PORT: u16 = 587;
 const SMTP_SUBMISSION_TLS_PORT: u16 = 465;
 const SMTP_TIMEOUT: u16 = 5;
+const SMTP_STATE_REFRESH_CUTOFF: Duration = Duration::from_secs(60 * 60 * 12);
 
 pub(crate) mod xoauth2;
 
@@ -203,6 +206,43 @@ pub struct SmtpEndpoint {
 }
 
 impl SmtpEndpoint {
+    fn get_access_token(
+        &self,
+        refresh_token: &str,
+        auth_method: &SmtpAuthMethod,
+    ) -> Result<xoauth2::TokenExchangeResult, Error> {
+        let client_id = ClientId::new(
+            self.config
+                .oauth2_client_id
+                .as_ref()
+                .ok_or_else(|| Error::Generic("oauth2-client-id not set".into()))?
+                .to_string(),
+        );
+        let client_secret = ClientSecret::new(
+            self.private_config
+                .oauth2_client_secret
+                .as_ref()
+                .ok_or_else(|| Error::Generic("oauth2-client-secret not set".into()))?
+                .to_string(),
+        );
+        let refresh_token = RefreshToken::new(refresh_token.into());
+
+        match auth_method {
+            SmtpAuthMethod::GoogleOAuth2 => {
+                xoauth2::get_google_token(client_id, client_secret, refresh_token)
+            }
+            SmtpAuthMethod::MicrosoftOAuth2 => xoauth2::get_microsoft_token(
+                client_id,
+                client_secret,
+                self.config.oauth2_tenant_id.as_ref().ok_or(Error::Generic(
+                    "tenant ID not set, required for Microsoft OAuth2".into(),
+                ))?,
+                refresh_token,
+            ),
+            _ => Err(Error::Generic("OAuth2 not configured".into())),
+        }
+    }
+
     fn build_transport(&self, tls: Tls, port: u16) -> Result<SmtpTransport, Error> {
         let mut transport_builder = SmtpTransport::builder_dangerous(&self.config.server)
             .tls(tls)
@@ -334,6 +374,44 @@ impl Endpoint for SmtpEndpoint {
     fn disabled(&self) -> bool {
         self.config.disable.unwrap_or_default()
     }
+
+    fn trigger_state_refresh(&self) -> Result<(), Error> {
+        let state = context().load_oauth_state(self.name())?;
+
+        let Some(refresh_token) = &state.oauth2_refresh_token else {
+            return Ok(());
+        };
+
+        // The intended callers are daily update jobs, so on a PVE cluster this function
+        // may be called once per node in a relatively short window. This cutoff prevents
+        // unnecessary token exchanges.
+        if SystemTime::now()
+            .duration_since(UNIX_EPOCH + Duration::from_secs(state.last_refreshed as u64))
+            .map_err(|e| Error::Generic(e.to_string()))?
+            < SMTP_STATE_REFRESH_CUTOFF
+        {
+            return Ok(());
+        }
+
+        let Some(auth_method) = self.config.auth_method.as_ref() else {
+            return Ok(());
+        };
+
+        let state = match self
+            .get_access_token(refresh_token, auth_method)?
+            .refresh_token
+        {
+            Some(tok) => state.set_oauth2_refresh_token(Some(tok.into_secret())), // New token was returned, rotate
+            None => state,
+        }
+        .set_last_refreshed(proxmox_time::epoch_i64());
+
+        context().save_oauth_state(self.name(), Some(state))?;
+
+        info!("OAuth2 state refreshed for endpoint `{}`", self.name());
+
+        Ok(())
+    }
 }
 
 /// Construct a lettre `Message` from a raw email message.
diff --git a/proxmox-notify/src/lib.rs b/proxmox-notify/src/lib.rs
index 619dd7db..ee4ffcd3 100644
--- a/proxmox-notify/src/lib.rs
+++ b/proxmox-notify/src/lib.rs
@@ -9,7 +9,7 @@ use context::context;
 use serde::{Deserialize, Serialize};
 use serde_json::json;
 use serde_json::Value;
-use tracing::{error, info};
+use tracing::{debug, error, info};
 
 use proxmox_schema::api;
 use proxmox_section_config::SectionConfigData;
@@ -169,6 +169,15 @@ pub trait Endpoint {
 
     /// Check if the endpoint is disabled
     fn disabled(&self) -> bool;
+
+    /// Refresh endpoint's state.
+    ///
+    /// Implementations may persist endpoint-internal state (e.g. SMTP XOAUTH2 refresh
+    /// tokens). Callers must hold the notifications config lock so that state files
+    /// cannot drift relative to concurrently edited/deleted configs.
+    fn trigger_state_refresh(&self) -> Result<(), Error> {
+        Ok(())
+    }
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -605,6 +614,23 @@ impl Bus {
 
         Ok(())
     }
+
+    /// Refresh all endpoints' internal state.
+    ///
+    /// The caller must hold a lock to the notifications config, see
+    /// [`Endpoint::trigger_state_refresh`]'s docs.
+    ///
+    /// This function works on a best effort basis, if an endpoint's state cannot
+    /// be updated for whatever reason, the error is logged and the next one(s)
+    /// are attempted.
+    pub fn trigger_state_refresh(&self) {
+        for (name, endpoint) in &self.endpoints {
+            match endpoint.trigger_state_refresh() {
+                Ok(()) => debug!("triggered state refresh for endpoint '{name}'"),
+                Err(e) => error!("could not trigger state refresh for endpoint '{name}': {e}"),
+            };
+        }
+    }
 }
 
 #[cfg(test)]
-- 
2.47.3