diff --git a/codex-rs/login/src/api_provision.rs b/codex-rs/login/src/api_provision.rs
index f018dc343d..50a3c775db 100644
--- a/codex-rs/login/src/api_provision.rs
+++ b/codex-rs/login/src/api_provision.rs
@@ -217,14 +217,19 @@ async fn exchange_authorization_code_for_tokens(
         client
             .request(Method::POST, &url)
             .header(reqwest::header::ACCEPT, "application/json")
+            .header(
+                reqwest::header::CONTENT_TYPE,
+                "application/x-www-form-urlencoded",
+            )
             .header(reqwest::header::USER_AGENT, USER_AGENT)
-            .json(&serde_json::json!({
-                "client_id": client_id,
-                "code_verifier": code_verifier,
-                "code": code,
-                "grant_type": "authorization_code",
-                "redirect_uri": redirect_uri,
-            })),
+            .body(format!(
+                "client_id={}&code_verifier={}&code={}&grant_type={}&redirect_uri={}",
+                urlencoding::encode(client_id),
+                urlencoding::encode(code_verifier),
+                urlencoding::encode(code),
+                urlencoding::encode("authorization_code"),
+                urlencoding::encode(redirect_uri)
+            )),
         "POST",
         &url,
     )
diff --git a/codex-rs/login/src/api_provision_tests.rs b/codex-rs/login/src/api_provision_tests.rs
index 84f9ee3055..9d42d83065 100644
--- a/codex-rs/login/src/api_provision_tests.rs
+++ b/codex-rs/login/src/api_provision_tests.rs
@@ -4,7 +4,8 @@ use serde_json::json;
 use wiremock::Mock;
 use wiremock::MockServer;
 use wiremock::ResponseTemplate;
-use wiremock::matchers::body_json;
+use wiremock::matchers::body_string_contains;
+use wiremock::matchers::header;
 use wiremock::matchers::method;
 use wiremock::matchers::path;
 use wiremock::matchers::query_param;
@@ -62,13 +63,14 @@ async fn provision_from_authorization_code_provisions_api_key() {
     let server = MockServer::start().await;
     Mock::given(method("POST"))
         .and(path("/oauth/token"))
-        .and(body_json(json!({
-            "client_id": "client-123",
-            "code_verifier": "verifier-123",
-            "code": "auth-code-123",
-            "grant_type": "authorization_code",
-            "redirect_uri": "http://localhost:5000/auth/callback",
-        })))
+        .and(header("content-type", "application/x-www-form-urlencoded"))
+        .and(body_string_contains("client_id=client-123"))
+        .and(body_string_contains("code_verifier=verifier-123"))
+        .and(body_string_contains("code=auth-code-123"))
+        .and(body_string_contains("grant_type=authorization_code"))
+        .and(body_string_contains(
+            "redirect_uri=http%3A%2F%2Flocalhost%3A5000%2Fauth%2Fcallback",
+        ))
         .respond_with(ResponseTemplate::new(200).set_body_json(json!({
             "id_token": "id-token-123",
             "access_token": "oauth-access-123",
diff --git a/codex-rs/tui/src/chatwidget/dotenv_api_key.rs b/codex-rs/tui/src/chatwidget/dotenv_api_key.rs
index 7717cf43b8..0d9ba67af2 100644
--- a/codex-rs/tui/src/chatwidget/dotenv_api_key.rs
+++ b/codex-rs/tui/src/chatwidget/dotenv_api_key.rs
@@ -12,9 +12,16 @@ use codex_login::OPENAI_API_KEY_ENV_VAR;
 
 pub(super) fn validate_dotenv_target(path: &Path) -> io::Result<()> {
     ensure_parent_dir(path)?;
+    reject_symlink(path)?;
 
     if path.exists() {
-        OpenOptions::new().append(true).open(path)?;
+        let mut options = OpenOptions::new();
+        options.append(true);
+        #[cfg(unix)]
+        {
+            options.custom_flags(libc::O_NOFOLLOW);
+        }
+        options.open(path)?;
         return Ok(());
     }
 
@@ -22,6 +29,7 @@ pub(super) fn validate_dotenv_target(path: &Path) -> io::Result<()> {
     options.write(true).create_new(true);
     #[cfg(unix)]
     {
+        options.custom_flags(libc::O_NOFOLLOW);
         options.mode(0o600);
     }
     options.open(path)?;
@@ -37,6 +45,7 @@ pub(super) fn upsert_dotenv_api_key(path: &Path, api_key: &str) -> io::Result<()
     }
 
     ensure_parent_dir(path)?;
+    reject_symlink(path)?;
 
     let existing = match std::fs::read_to_string(path) {
         Ok(contents) => contents,
@@ -70,10 +79,13 @@ pub(super) fn upsert_dotenv_api_key(path: &Path, api_key: &str) -> io::Result<()
 }
 
 fn write_dotenv_file(path: &Path, contents: &str) -> io::Result<()> {
+    reject_symlink(path)?;
+
     let mut options = OpenOptions::new();
     options.write(true).create(true).truncate(true);
     #[cfg(unix)]
     {
+        options.custom_flags(libc::O_NOFOLLOW);
         options.mode(0o600);
     }
 
@@ -89,6 +101,23 @@ fn write_dotenv_file(path: &Path, contents: &str) -> io::Result<()> {
     Ok(())
 }
 
+fn reject_symlink(path: &Path) -> io::Result<()> {
+    let metadata = match std::fs::symlink_metadata(path) {
+        Ok(metadata) => metadata,
+        Err(err) if err.kind() == ErrorKind::NotFound => return Ok(()),
+        Err(err) => return Err(err),
+    };
+
+    if metadata.file_type().is_symlink() {
+        return Err(io::Error::new(
+            ErrorKind::InvalidInput,
+            ".env.local must not be a symlink",
+        ));
+    }
+
+    Ok(())
+}
+
 fn ensure_parent_dir(path: &Path) -> io::Result<()> {
     if let Some(parent) = path.parent() {
         std::fs::create_dir_all(parent)?;
@@ -154,6 +183,22 @@ mod tests {
         assert_eq!(mode, 0o600);
     }
 
+    #[cfg(unix)]
+    #[test]
+    fn upsert_rejects_symlink_target() {
+        let temp_dir = tempdir().expect("tempdir");
+        let dotenv_path = temp_dir.path().join(".env");
+        let target_path = temp_dir.path().join("target.env");
+        std::fs::write(&target_path, "OTHER=value\n").expect("seed target");
+        std::os::unix::fs::symlink(&target_path, &dotenv_path).expect("symlink");
+
+        let err = upsert_dotenv_api_key(&dotenv_path, "sk-test-key").expect_err("reject symlink");
+
+        assert_eq!(err.kind(), ErrorKind::InvalidInput);
+        let target = std::fs::read_to_string(&target_path).expect("read target");
+        assert_eq!(target, "OTHER=value\n");
+    }
+
     #[test]
     fn upsert_replaces_existing_api_key_and_collapses_duplicates() {
         let temp_dir = tempdir().expect("tempdir");