refactor(mcp/v2): drop mis-modeled PerUserEnvVar api_key key_source

Per-user env-vars are templated static headers (resolved alongside auth via the static-headers
path), not an api_key credential mode; the PerUserEnvVar key_source was unreachable (no server
config maps to it) and contradicted that model. ApiKeySource is now SharedKey | Byok and the
api_key arm matches the two real sources. Static/env-var header resolution reuses v1's
_resolve_static_headers_with_env_vars at the v2 manager (step 6); the clean v2 rewrite lands at v1
retirement alongside the caching model.

litellm/proxy/gateway/mcp/outbound_credentials/resolver.py

@@ -44,7 +44,6 @@ from .types import (
     CredError,
     NoneConfig,
     PassthroughConfig,
-    PerUserEnvVar,
     ServerSpec,
     SharedKey,
     Subject,
@@ -112,18 +111,6 @@ class UpstreamCredentialProvider:
                 # The shared key is read straight from ServerSpec.config, not the per-user
                 # store; it is the same credential for every caller.
                 return Ok(_api_key_auth(config, source.value.get_secret_value()))
-            case PerUserEnvVar():
-                fetched = await self._per_user_value(subject, server)
-                if isinstance(fetched, Error):
-                    return Error(fetched.error)  # store/DB down -> 503
-                value = fetched.ok
-                if value is None:
-                    return Error(
-                        CredError.of_precondition_required(
-                            "api_key: per-user env var not set for this subject"
-                        )
-                    )
-                return Ok(_api_key_auth(config, value))
             case Byok():
                 fetched = await self._per_user_value(subject, server)
                 if isinstance(fetched, Error):

litellm/proxy/gateway/mcp/outbound_credentials/types.py

@@ -188,15 +188,6 @@ class SharedKey(BaseModel):
     value: SecretStr
 
 
-class PerUserEnvVar(BaseModel):
-    """A per-user value the admin templated as an env var; the user fills it in. Pulled from
-    the credential store at resolve time. Missing means the user has not completed setup, a
-    precondition (412) rather than an auth failure."""
-
-    model_config = ConfigDict(frozen=True)
-    source: Literal["per_user_env_var"] = "per_user_env_var"
-
-
 class Byok(BaseModel):
     """A key the user brings via the entry flow, stored per-user. Pulled from the credential
     store at resolve time. Missing means the user must provide it, a 401 + WWW-Authenticate
@@ -206,9 +197,7 @@ class Byok(BaseModel):
     source: Literal["byok"] = "byok"
 
 
-ApiKeySource = Annotated[
-    SharedKey | PerUserEnvVar | Byok, Field(discriminator="source")
-]
+ApiKeySource = Annotated[SharedKey | Byok, Field(discriminator="source")]
 
 
 class ApiKeyConfig(BaseModel):

tests/mcp_tests/gateway/test_resolver.py

@@ -59,7 +59,6 @@ from litellm.proxy.gateway.mcp.outbound_credentials.types import (
     CredError,
     NoneConfig,
     PassthroughConfig,
-    PerUserEnvVar,
     ServerSpec,
     SharedKey,
     StaticKeys,
@@ -295,13 +294,12 @@ def test_secret_fields_are_masked_in_serialization():
     assert config.key_source.value.get_secret_value() == "SUPER-SECRET"
 
 
-@pytest.mark.parametrize("source", [Byok(), PerUserEnvVar()])
-async def test_api_key_per_user_pulls_the_subject_credential(source: object):
+async def test_api_key_byok_pulls_the_subject_credential():
     store = InMemoryCredentialStore(
         {CredentialKey(tenant_id="t1", subject_id="u1", server_id="s1"): "user-secret"}
     )
     provider = _provider(credential_store=store)
-    result = await provider.resolve(SUBJECT, _spec(ApiKeyConfig(key_source=source)))  # type: ignore[arg-type]
+    result = await provider.resolve(SUBJECT, _spec(ApiKeyConfig(key_source=Byok())))
     assert isinstance(result, Ok)
     assert _applied_headers(result.ok)["Authorization"] == "Bearer user-secret"
 
@@ -313,15 +311,6 @@ async def test_api_key_byok_missing_returns_unauthorized():
     assert result.error.tag == "unauthorized"
 
 
-async def test_api_key_env_var_missing_returns_precondition_required():
-    # Missing per-user env var -> 412 (a setup precondition), distinct from BYOK's 401.
-    result = await PROVIDER.resolve(
-        SUBJECT, _spec(ApiKeyConfig(key_source=PerUserEnvVar()))
-    )
-    assert isinstance(result, Error)
-    assert result.error.tag == "precondition_required"
-
-
 async def test_api_key_per_user_isolated_by_subject():
     # The stored key belongs to (t1,u1,s1); a different subject must not receive it.
     store = InMemoryCredentialStore(