add legacy element hack for UIAA using invalid user field

see:
- e9302a9556
- https://github.com/element-hq/element-android/issues/8043
- https://github.com/element-hq/element-ios/issues/7405

Signed-off-by: strawberry <strawberry@puppygock.gay>

src/main/Cargo.toml

@@ -67,6 +67,7 @@ dev_release_log_level = [
 ]
 element_hacks = [
 	"conduit-api/element_hacks",
+	"conduit-service/element_hacks",
 ]
 gzip_compression = [
 	"conduit-api/gzip_compression",

src/service/Cargo.toml

@@ -17,6 +17,7 @@ crate-type = [
 ]
 
 [features]
+element_hacks = []
 dev_release_log_level = []
 release_max_log_level = [
 	"tracing/max_level_trace",

src/service/uiaa/mod.rs

@@ -58,9 +58,22 @@ impl Service {
 			AuthData::Password(Password {
 				identifier,
 				password,
+				#[cfg(feature = "element_hacks")]
+				user,
 				..
 			}) => {
-				let UserIdentifier::UserIdOrLocalpart(username) = identifier else {
+				#[cfg(feature = "element_hacks")]
+				let username = if let Some(UserIdentifier::UserIdOrLocalpart(username)) = identifier {
+					username
+				} else if let Some(username) = user {
+					username
+				} else {
+					return Err(Error::BadRequest(ErrorKind::Unrecognized, "Identifier type not recognized."));
+				};
+
+				#[cfg(not(feature = "element_hacks"))]
+				let Some(UserIdentifier::UserIdOrLocalpart(username)) = identifier
+				else {
 					return Err(Error::BadRequest(ErrorKind::Unrecognized, "Identifier type not recognized."));
 				};