melib/imap: impl AUTH=ANONYMOUS (RFC4505)

Signed-off-by: Manos Pitsidianakis <manos@pitsidianak.is>

meli/docs/meli.1

@@ -803,6 +803,14 @@ Mailcap entries are searched for in the following files, in this order:
 .Re
 .It
 .Rs
+.%B RFC4505 Anonymous Simple Authentication and Security Layer (SASL) Mechanism
+.%I IETF
+.%D June 12, 2006
+.%A Kurt Zeilenga
+.%U https://datatracker.ietf.org/doc/rfc4505/
+.Re
+.It
+.Rs
 .%B RFC4549 Synchronization Operations for Disconnected IMAP4 Clients
 .%I IETF
 .%D June 16, 2006

meli/docs/meli.conf.5

@@ -455,6 +455,12 @@ For help on setup with
 .Tn Gmail
 section below.
 .Pq Em false \" default value
+.It Ic use_auth_anonymous Ar boolean
+.Pq Em optional
+Use
+.Em AUTH=ANONYMOUS
+extension for authentication.
+.Pq Em false \" default value
 .It Ic timeout Ar integer
 .Pq Em optional
 Timeout to use for server connections in seconds.

melib/src/imap/connection.rs

@@ -94,7 +94,9 @@ pub enum ImapProtocol {
 }
 
 #[derive(Clone, Copy, Debug)]
+#[non_exhaustive]
 pub struct ImapExtensionUse {
+    pub auth_anonymous: bool,
     pub condstore: bool,
     pub idle: bool,
     pub deflate: bool,
@@ -104,6 +106,7 @@ pub struct ImapExtensionUse {
 impl Default for ImapExtensionUse {
     fn default() -> Self {
         Self {
+            auth_anonymous: false,
             condstore: true,
             idle: true,
             deflate: true,
@@ -425,6 +428,29 @@ impl ImapStream {
                 ))
                 .await?;
             }
+            ImapProtocol::IMAP {
+                extension_use: ImapExtensionUse { auth_anonymous, .. },
+            } if auth_anonymous => {
+                if !capabilities
+                    .iter()
+                    .any(|cap| cap.eq_ignore_ascii_case(b"AUTH=ANONYMOUS"))
+                {
+                    return Err(Error::new(format!(
+                        "Could not connect to {}: AUTH=ANONYMOUS is enabled but server did not \
+                         return AUTH=ANONYMOUS capability. Returned capabilities were: {}",
+                        &server_conf.server_hostname,
+                        capabilities
+                            .iter()
+                            .map(|capability| String::from_utf8_lossy(capability).to_string())
+                            .collect::<Vec<String>>()
+                            .join(" ")
+                    ))
+                    .set_kind(ErrorKind::Authentication));
+                }
+                ret.send_command_raw(b"AUTHENTICATE ANONYMOUS").await?;
+                ret.wait_for_continuation_request().await?;
+                ret.send_literal(b"c2lyaGM=").await?;
+            }
             _ => {
                 let username = AString::try_from(server_conf.server_username.as_str())
                     .chain_err_kind(ErrorKind::Bug)?;
@@ -724,6 +750,7 @@ impl ImapConnection {
                             deflate,
                             idle: _idle,
                             oauth2: _,
+                            auth_anonymous: _,
                         },
                 } => {
                     if capabilities.contains(&b"CONDSTORE"[..]) && condstore {

melib/src/imap/mod.rs

@@ -79,6 +79,7 @@ pub type UIDVALIDITY = UID;
 pub type MessageSequenceNumber = ImapNum;
 
 pub static SUPPORTED_CAPABILITIES: &[&str] = &[
+    "AUTH=ANONYMOUS",
     "AUTH=OAUTH2",
     "COMPRESS=DEFLATE",
     "CONDSTORE",
@@ -257,6 +258,7 @@ impl MailBackend for ImapType {
                     deflate,
                     condstore,
                     oauth2,
+                    auth_anonymous,
                 },
         } = self.server_conf.protocol
         {
@@ -298,6 +300,15 @@ impl MailBackend for ImapType {
                             };
                         }
                     }
+                    "AUTH=ANONYMOUS" => {
+                        if auth_anonymous {
+                            *status = MailBackendExtensionStatus::Enabled { comment: None };
+                        } else {
+                            *status = MailBackendExtensionStatus::Supported {
+                                comment: Some("Disabled by user configuration"),
+                            };
+                        }
+                    }
                     _ => {
                         if SUPPORTED_CAPABILITIES
                             .iter()
@@ -1339,6 +1350,7 @@ impl ImapType {
                     condstore: get_conf_val!(s["use_condstore"], true)?,
                     deflate: get_conf_val!(s["use_deflate"], true)?,
                     oauth2: use_oauth2,
+                    auth_anonymous: get_conf_val!(s["use_auth_anonymous"], false)?,
                 },
             },
             timeout,
@@ -1608,6 +1620,7 @@ impl ImapType {
         get_conf_val!(s["use_idle"], true)?;
         get_conf_val!(s["use_condstore"], true)?;
         get_conf_val!(s["use_deflate"], true)?;
+        get_conf_val!(s["use_auth_anonymous"], false)?;
         let _timeout = get_conf_val!(s["timeout"], 16_u64)?;
         let extra_keys = s
             .extra