Fix clearing credentials (#12041)

### Related

* Closes RR-3070

### What

Makes clearing the credentials actually remove the saved credentials

Author: IsseW

crates/utils/re_auth/src/oauth.rs

@@ -48,6 +48,16 @@ pub fn load_credentials() -> Result<Option<Credentials>, CredentialsLoadError> {
     }
 }
 
+#[derive(Debug, thiserror::Error)]
+#[error("failed to load credentials: {0}")]
+pub struct CredentialsClearError(#[from] storage::ClearError);
+
+pub fn clear_credentials() -> Result<(), CredentialsClearError> {
+    storage::clear()?;
+
+    Ok(())
+}
+
 #[derive(Debug, thiserror::Error)]
 pub enum CredentialsRefreshError {
     #[error("failed to refresh credentials: {0}")]

crates/utils/re_auth/src/oauth/storage.rs

@@ -36,15 +36,29 @@ pub enum StoreError {
     NoLocalStorage,
 }
 
+#[derive(Debug, thiserror::Error)]
+pub enum ClearError {
+    #[error("failed to clear credentials: {0}")]
+    Io(#[from] std::io::Error),
+
+    #[cfg(not(target_arch = "wasm32"))]
+    #[error("could not find a valid config location, please ensure $HOME is set")]
+    UnknownConfigLocation,
+
+    #[cfg(target_arch = "wasm32")]
+    #[error("failed to get window.localStorage")]
+    NoLocalStorage,
+}
+
 #[cfg(not(target_arch = "wasm32"))]
-pub use file::{load, store};
+pub use file::{clear, load, store};
 
 #[cfg(target_arch = "wasm32")]
-pub use web::{load, store};
+pub use web::{clear, load, store};
 
 #[cfg(not(target_arch = "wasm32"))]
 mod file {
-    use super::{Credentials, LoadError, StoreError};
+    use super::{ClearError, Credentials, LoadError, StoreError};
     use std::path::PathBuf;
 
     fn credentials_path() -> Option<PathBuf> {
@@ -71,13 +85,24 @@ mod file {
         std::fs::write(path, data)?;
         Ok(())
     }
+
+    pub fn clear() -> Result<(), ClearError> {
+        let path = credentials_path().ok_or(ClearError::UnknownConfigLocation)?;
+
+        match std::fs::remove_file(path) {
+            Ok(()) => Ok(()),
+            // If the file didn't exist this isn't a failure.
+            Err(err) if err.kind() == std::io::ErrorKind::NotFound => Ok(()),
+            Err(err) => Err(ClearError::Io(err)),
+        }
+    }
 }
 
 #[cfg(target_arch = "wasm32")]
 mod web {
     use wasm_bindgen::JsCast as _;
 
-    use super::{Credentials, LoadError, StoreError};
+    use super::{ClearError, Credentials, LoadError, StoreError};
 
     const STORAGE_KEY: &str = "rerun_auth";
 
@@ -95,6 +120,12 @@ mod web {
         }
     }
 
+    impl From<NoLocalStorage> for ClearError {
+        fn from(_: NoLocalStorage) -> Self {
+            Self::NoLocalStorage
+        }
+    }
+
     #[expect(clippy::needless_pass_by_value)]
     pub fn string_from_js_value(s: wasm_bindgen::JsValue) -> String {
         // it's already a string
@@ -140,4 +171,12 @@ mod web {
             .map_err(|err| std::io::Error::other(string_from_js_value(err)))?;
         Ok(())
     }
+
+    pub fn clear() -> Result<(), ClearError> {
+        let local_storage = get_local_storage()?;
+        local_storage
+            .remove_item(STORAGE_KEY)
+            .map_err(|err| std::io::Error::other(string_from_js_value(err)))?;
+        Ok(())
+    }
 }

crates/viewer/re_redap_browser/src/server_modal.rs

@@ -369,8 +369,15 @@ fn auth_ui(ui: &mut egui::Ui, cmd: &CommandSender, auth: &mut Authentication) {
                         .on_hover_text("Clear login status")
                         .clicked()
                     {
-                        auth.error = None;
-                        auth.start_login_flow(ui);
+                        match re_auth::oauth::clear_credentials() {
+                            Ok(()) => {
+                                auth.email = None;
+                                auth.start_login_flow(ui);
+                            }
+                            Err(err) => {
+                                auth.error = Some(err.to_string());
+                            }
+                        }
                     }
                 } else if auth.error.is_some() {
                     if ui