diff --git a/services/backup/src/http/handlers/backup.rs b/services/backup/src/http/handlers/backup.rs
--- a/services/backup/src/http/handlers/backup.rs
+++ b/services/backup/src/http/handlers/backup.rs
@@ -12,11 +12,14 @@
   },
   http::{
     auth_service::Authenticated,
-    multipart::{get_named_text_field, get_text_field},
+    multipart::{
+      get_all_remaining_fields, get_named_text_field, get_text_field,
+      parse_bytes_to_string,
+    },
   },
   tools::Defer,
 };
-use std::convert::Infallible;
+use std::{collections::HashMap, convert::Infallible};
 use tokio_stream::{wrappers::ReceiverStream, StreamExt};
 use tracing::{info, instrument, trace, warn};
 
@@ -49,7 +52,8 @@
   let (attachments, attachments_revokes) =
     multipart.process_attachmens_field(&blob_client).await?;
 
-  let siwe_backup_msg = multipart.get_siwe_backup_msg().await?;
+  let aux_data = multipart.get_aux_data().await?;
+  let siwe_backup_msg = aux_data.get_siwe_backup_msg()?;
 
   let item = BackupItem::new(
     user.user_id.clone(),
@@ -326,7 +330,8 @@
     .forward_field_to_blob(blob_client, "user_keys_hash", "user_keys")
     .await?;
 
-  let siwe_backup_msg = multipart.get_siwe_backup_msg().await?;
+  let aux_data = multipart.get_aux_data().await?;
+  let siwe_backup_msg = aux_data.get_siwe_backup_msg()?;
   let ordered_backup_item = db_client
     .find_last_backup_item(user_id)
     .await
@@ -453,9 +458,6 @@
     data_field_name: &str,
   ) -> actix_web::Result<(BlobInfo, Defer<'revoke>)>;
 
-  /// Consumes a text field named `siwe_backup_msg`
-  async fn get_siwe_backup_msg(&mut self) -> actix_web::Result<Option<String>>;
-
   /// Consumes a text field named `attachments`.
   /// For each attachment hash, establishes a new blob holder.
   /// Returns BlobInfos and a revoke handle for removing the holder
@@ -465,6 +467,9 @@
     &mut self,
     blob_client: &'blob BlobServiceClient,
   ) -> Result<(Vec<BlobInfo>, Vec<Defer<'revoke>>), BackupError>;
+
+  /// Consumes all remaining fields and stores them in [`BackupAuxFields`]
+  async fn get_aux_data(&mut self) -> actix_web::Result<BackupAuxFields>;
 }
 
 impl BackupRequestInput for actix_multipart::Multipart {
@@ -539,16 +544,6 @@
     Ok((blob_info, revoke_holder))
   }
 
-  #[instrument(skip_all)]
-  async fn get_siwe_backup_msg(&mut self) -> actix_web::Result<Option<String>> {
-    Ok(
-      get_text_field(self)
-        .await?
-        .filter(|(name, _)| name == "siwe_backup_msg")
-        .map(|(_, siwe_backup_msg)| siwe_backup_msg),
-    )
-  }
-
   #[instrument(skip_all)]
   async fn process_attachmens_field<'revoke, 'blob: 'revoke>(
     &mut self,
@@ -573,6 +568,24 @@
     blob_utils::create_holders_for_blob_hashes(attachments_hashes, blob_client)
       .await
   }
+
+  async fn get_aux_data(&mut self) -> actix_web::Result<BackupAuxFields> {
+    let field_map = get_all_remaining_fields(self).await?;
+    Ok(BackupAuxFields(field_map))
+  }
+}
+
+struct BackupAuxFields(HashMap<String, Vec<u8>>);
+
+impl BackupAuxFields {
+  fn get_siwe_backup_msg(&self) -> actix_web::Result<Option<String>> {
+    let Some(buf) = self.0.get("siwe_backup_msg") else {
+      return Ok(None);
+    };
+
+    let siwe_backup_msg = parse_bytes_to_string(buf.clone())?;
+    Ok(Some(siwe_backup_msg))
+  }
 }
 
 mod blob_utils {
diff --git a/shared/comm-lib/src/http/multipart.rs b/shared/comm-lib/src/http/multipart.rs
--- a/shared/comm-lib/src/http/multipart.rs
+++ b/shared/comm-lib/src/http/multipart.rs
@@ -1,3 +1,5 @@
+use std::collections::HashMap;
+
 use actix_multipart::{Field, MultipartError};
 use actix_web::error::{ErrorBadRequest, ParseError};
 use tokio_stream::StreamExt;
@@ -36,8 +38,7 @@
     buf.extend_from_slice(&chunk);
   }
 
-  let text =
-    String::from_utf8(buf).map_err(|err| ParseError::Utf8(err.utf8_error()))?;
+  let text = parse_bytes_to_string(buf)?;
 
   Ok(Some((name, text)))
 }
@@ -58,3 +59,28 @@
 
   Ok(backup_id)
 }
+
+pub async fn get_all_remaining_fields(
+  multipart: &mut actix_multipart::Multipart,
+) -> Result<std::collections::HashMap<String, Vec<u8>>, MultipartError> {
+  let mut found_fields = HashMap::new();
+
+  while let Some(mut field) = multipart.try_next().await? {
+    let name = field.name().to_string();
+    let mut buf = Vec::new();
+    while let Some(chunk) = field.try_next().await? {
+      buf.extend_from_slice(&chunk);
+    }
+    found_fields.insert(name, buf);
+  }
+
+  Ok(found_fields)
+}
+
+pub fn parse_bytes_to_string(
+  utf8_buffer: Vec<u8>,
+) -> Result<String, MultipartError> {
+  let parsed_string = String::from_utf8(utf8_buffer)
+    .map_err(|err| ParseError::Utf8(err.utf8_error()))?;
+  Ok(parsed_string)
+}