[PATCH proxmox 5/7] notify (smtp): Add state handling logic

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

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

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

Signed-off-by: Arthur Bied-Charreton <a.bied-charreton@proxmox.com>
---
 proxmox-notify/src/api/common.rs     | 16 ++++++
 proxmox-notify/src/api/smtp.rs       | 29 ++++++++++-
 proxmox-notify/src/endpoints/smtp.rs | 75 +++++++++++++++++++++++++++-
 proxmox-notify/src/lib.rs            | 19 +++++++
 4 files changed, 137 insertions(+), 2 deletions(-)

diff --git a/proxmox-notify/src/api/common.rs b/proxmox-notify/src/api/common.rs
index fa2356e2..1e6b7d46 100644
--- a/proxmox-notify/src/api/common.rs
+++ b/proxmox-notify/src/api/common.rs
@@ -3,6 +3,22 @@ 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.
+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 4231cdae..8992e789 100644
--- a/proxmox-notify/src/api/smtp.rs
+++ b/proxmox-notify/src/api/smtp.rs
@@ -2,7 +2,7 @@ use proxmox_http_error::HttpError;
 
 use crate::api::{http_bail, http_err};
 use crate::endpoints::smtp::{
-    DeleteableSmtpProperty, SmtpConfig, SmtpConfigUpdater, SmtpPrivateConfig,
+    self, DeleteableSmtpProperty, SmtpConfig, SmtpConfigUpdater, SmtpPrivateConfig,
     SmtpPrivateConfigUpdater, SMTP_TYPENAME,
 };
 use crate::Config;
@@ -69,6 +69,16 @@ pub fn add_endpoint(
         &endpoint_config.name,
     )?;
 
+    smtp::State::new(oauth2_refresh_token)
+        .store(&endpoint_config.name)
+        .map_err(|e| {
+            http_err!(
+                INTERNAL_SERVER_ERROR,
+                "could not create state file for endpoint '{}': {e}",
+                endpoint_config.name
+            )
+        })?;
+
     config
         .config
         .set_data(&endpoint_config.name, SMTP_TYPENAME, &endpoint_config)
@@ -206,6 +216,23 @@ pub fn update_endpoint(
         }
     })?;
 
+    smtp::State::load(name)
+        .map_err(|e| {
+            http_err!(
+                INTERNAL_SERVER_ERROR,
+                "could not load state for endpoint '{name}': {e}"
+            )
+        })?
+        .set_oauth2_refresh_token(oauth2_refresh_token)
+        .set_last_refreshed(proxmox_time::epoch_i64())
+        .store(name)
+        .map_err(|e| {
+            http_err!(
+                INTERNAL_SERVER_ERROR,
+                "could not persist state for endpoint '{name}': {e}"
+            )
+        })?;
+
     config
         .config
         .set_data(name, SMTP_TYPENAME, &endpoint)
diff --git a/proxmox-notify/src/endpoints/smtp.rs b/proxmox-notify/src/endpoints/smtp.rs
index 361c4da9..244799fd 100644
--- a/proxmox-notify/src/endpoints/smtp.rs
+++ b/proxmox-notify/src/endpoints/smtp.rs
@@ -1,12 +1,15 @@
 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::authentication::{Credentials, Mechanism};
 use lettre::transport::smtp::client::{Tls, TlsParameters};
 use lettre::{message::header::ContentType, Message, SmtpTransport, Transport};
 use serde::{Deserialize, Serialize};
 
+use oauth2::{ClientId, ClientSecret, RefreshToken};
+
 use proxmox_schema::api_types::COMMENT_SCHEMA;
 use proxmox_schema::{api, Updater};
 
@@ -22,6 +25,7 @@ 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_SECONDS: u64 = 60 * 60 * 12;
 
 mod state;
 mod xoauth2;
@@ -205,6 +209,43 @@ 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)
@@ -336,6 +377,38 @@ impl Endpoint for SmtpEndpoint {
     fn disabled(&self) -> bool {
         self.config.disable.unwrap_or_default()
     }
+
+    fn trigger_state_refresh(&self) -> Result<(), Error> {
+        let state = State::load(self.name())?;
+
+        let Some(refresh_token) = &state.oauth2_refresh_token else {
+            return Ok(());
+        };
+
+        // The refresh job is configured in pveupdate, which runs once for each node.
+        // Don't refresh if we already did it recently.
+        if SystemTime::now()
+            .duration_since(UNIX_EPOCH + Duration::from_secs(state.last_refreshed as u64))
+            .map_err(|e| Error::Generic(e.to_string()))?
+            < Duration::from_secs(SMTP_STATE_REFRESH_CUTOFF_SECONDS)
+        {
+            return Ok(());
+        }
+
+        let Some(auth_method) = self.config.auth_method.as_ref() else {
+            return Ok(());
+        };
+
+        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())
+        .store(self.name())
+    }
 }
 
 /// Construct a lettre `Message` from a raw email message.
diff --git a/proxmox-notify/src/lib.rs b/proxmox-notify/src/lib.rs
index 879f8326..c1a5e535 100644
--- a/proxmox-notify/src/lib.rs
+++ b/proxmox-notify/src/lib.rs
@@ -157,6 +157,11 @@ pub trait Endpoint {
 
     /// Check if the endpoint is disabled
     fn disabled(&self) -> bool;
+
+    /// Refresh endpoint's state
+    fn trigger_state_refresh(&self) -> Result<(), Error> {
+        Ok(())
+    }
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -593,6 +598,20 @@ impl Bus {
 
         Ok(())
     }
+
+    /// Refresh all endpoints' internal state.
+    ///
+    /// 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(()) => info!("triggered state refresh for endpoint '{name}'"),
+                Err(e) => error!("could not trigger state refresh for endpoint '{name}': {e}"),
+            };
+        }
+    }
 }
 
 #[cfg(test)]
-- 
2.47.3