feat(unstable): Remove unused auth_methods from Error type (#708)

Author: benbrandt

docs/protocol/draft/schema.mdx

@@ -2501,27 +2501,18 @@ See protocol docs: [JSON-RPC Error Object](https://www.jsonrpc.org/specification
 
 **Properties:**
 
-<ResponseField name="authMethods" type={<a href="#authmethod">AuthMethod[]</a>} >
-  **UNSTABLE**
-
-This capability is not part of the spec yet, and may be removed or changed at any point.
-
-Authentication methods relevant to this error.
-Typically included with `AUTH_REQUIRED` errors to narrow down which
-authentication methods are applicable from those shared during initialization.
-
-</ResponseField>
 <ResponseField name="code" type={<a href="#errorcode">ErrorCode</a>} required>
-  A number indicating the error type that occurred.
-This must be an integer as defined in the JSON-RPC specification.
+  A number indicating the error type that occurred. This must be an integer as
+  defined in the JSON-RPC specification.
 </ResponseField>
-<ResponseField name="data" type={"object"} >
-  Optional primitive or structured value that contains additional information about the error.
-This may include debugging information or context-specific details.
+<ResponseField name="data" type={"object"}>
+  Optional primitive or structured value that contains additional information
+  about the error. This may include debugging information or context-specific
+  details.
 </ResponseField>
 <ResponseField name="message" type={"string"} required>
-  A string providing a short description of the error.
-The message should be limited to a concise single sentence.
+  A string providing a short description of the error. The message should be
+  limited to a concise single sentence.
 </ResponseField>
 
 ## <span class="font-mono">ErrorCode</span>

docs/rfds/auth-methods.mdx

@@ -152,29 +152,6 @@ Because `terminal` auth methods require specific client-side support, clients mu
 
 The `env_var` type does not require a capability opt-in since any client can set environment variables when starting a process, we are just providing additional context for the environment variable.
 
-### Auth errors
-
-It might be useful to include a list of AuthMethod ids to the AUTH_REQUIRED JsonRpc error. Why do we need this if they're already shared during `initialize`:
-All supported auth methods are shared during `initialize`. When user starts a session, they've already selected a model, which can narrow down a list of options.
-
-```json
-{
-  "jsonrpc": "2.0",
-  "id": 2,
-  "error": {
-    "code": -32000,
-    "message": "Authentication required",
-    "authMethods": [
-      {
-        "id": "chatgpt",
-        "name": "Login with ChatGPT",
-        "description": "Use your ChatGPT login with Codex CLI (requires a paid ChatGPT subscription)"
-      }
-    ]
-  }
-}
-```
-
 ## Frequently asked questions
 
 > What questions have arisen over the course of authoring this document or during subsequent discussions?
@@ -189,6 +166,7 @@ There is also an alternative to adding a separate `elicitation` capability, whic
 
 There was a part about elicitations https://github.com/agentclientprotocol/agent-client-protocol/blob/939ef116a1b14016e4e3808b8764237250afa253/docs/rfds/auth.mdx removed it for now, will move to a separate rfd
 
+- 2026-03-09: Remove auth_methods from Error type
 - 2026-03-03: Changed `env_var` from single `varName` to structured `vars` array of `AuthEnvVar` objects; simplified field name from `varName` to `name`
 - 2026-02-27: Updated to reflect current implementation
 - 2026-01-14: Updates based on Core Maintainer discussion

schema/schema.unstable.json

@@ -1442,13 +1442,6 @@
     "Error": {
       "description": "JSON-RPC error object.\n\nRepresents an error that occurred during method execution, following the\nJSON-RPC 2.0 error object specification with optional additional data.\n\nSee protocol docs: [JSON-RPC Error Object](https://www.jsonrpc.org/specification#error_object)",
       "properties": {
-        "authMethods": {
-          "description": "**UNSTABLE**\n\nThis capability is not part of the spec yet, and may be removed or changed at any point.\n\nAuthentication methods relevant to this error.\nTypically included with `AUTH_REQUIRED` errors to narrow down which\nauthentication methods are applicable from those shared during initialization.",
-          "items": {
-            "$ref": "#/$defs/AuthMethod"
-          },
-          "type": "array"
-        },
         "code": {
           "allOf": [
             {

src/error.rs

@@ -38,16 +38,6 @@ pub struct Error {
     /// This may include debugging information or context-specific details.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub data: Option<serde_json::Value>,
-    /// **UNSTABLE**
-    ///
-    /// This capability is not part of the spec yet, and may be removed or changed at any point.
-    ///
-    /// Authentication methods relevant to this error.
-    /// Typically included with `AUTH_REQUIRED` errors to narrow down which
-    /// authentication methods are applicable from those shared during initialization.
-    #[cfg(feature = "unstable_auth_methods")]
-    #[serde(default, skip_serializing_if = "Vec::is_empty", rename = "authMethods")]
-    pub auth_methods: Vec<crate::AuthMethod>,
 }
 
 impl Error {
@@ -60,8 +50,6 @@ impl Error {
             code: code.into(),
             message: message.into(),
             data: None,
-            #[cfg(feature = "unstable_auth_methods")]
-            auth_methods: Vec::new(),
         }
     }
 
@@ -125,20 +113,6 @@ impl Error {
         ErrorCode::AuthRequired.into()
     }
 
-    /// **UNSTABLE**
-    ///
-    /// This capability is not part of the spec yet, and may be removed or changed at any point.
-    ///
-    /// Authentication methods relevant to this error.
-    /// Typically included with `AUTH_REQUIRED` errors to narrow down which
-    /// authentication methods are applicable from those shared during initialization.
-    #[cfg(feature = "unstable_auth_methods")]
-    #[must_use]
-    pub fn auth_methods(mut self, auth_methods: Vec<crate::AuthMethod>) -> Self {
-        self.auth_methods = auth_methods;
-        self
-    }
-
     /// A given resource, such as a file, was not found.
     #[must_use]
     pub fn resource_not_found(uri: Option<String>) -> Self {
@@ -312,16 +286,6 @@ impl Display for Error {
             write!(f, ": {pretty}")?;
         }
 
-        #[cfg(feature = "unstable_auth_methods")]
-        if !self.auth_methods.is_empty() {
-            let ids: Vec<&str> = self
-                .auth_methods
-                .iter()
-                .map(|m| m.id().0.as_ref())
-                .collect();
-            write!(f, " (auth methods: {})", ids.join(", "))?;
-        }
-
         Ok(())
     }
 }
@@ -379,36 +343,4 @@ mod tests {
             );
         }
     }
-
-    #[cfg(feature = "unstable_auth_methods")]
-    #[test]
-    fn serialize_error_auth_methods() {
-        use crate::{AuthMethod, AuthMethodAgent};
-
-        // Verify auth_methods is omitted when empty
-        let err = Error::auth_required();
-        let json = serde_json::to_value(&err).unwrap();
-        assert!(
-            !json.as_object().unwrap().contains_key("authMethods"),
-            "authMethods should be omitted when empty"
-        );
-
-        // Verify auth_methods round-trips when present
-        let err = Error::auth_required().auth_methods(vec![AuthMethod::Agent(
-            AuthMethodAgent::new("api-key", "API Key"),
-        )]);
-        let json = serde_json::to_value(&err).unwrap();
-        assert!(
-            json.as_object().unwrap().contains_key("authMethods"),
-            "authMethods should be present"
-        );
-        assert_eq!(json["authMethods"].as_array().unwrap().len(), 1);
-        assert_eq!(json["authMethods"][0]["id"], "api-key");
-        assert_eq!(json["authMethods"][0]["name"], "API Key");
-
-        // Verify deserialization
-        let deserialized: Error = serde_json::from_value(json).unwrap();
-        assert_eq!(deserialized.auth_methods.len(), 1);
-        assert_eq!(deserialized.auth_methods[0].id().0.as_ref(), "api-key");
-    }
 }