diff --git a/src/adcp/server/auth.py b/src/adcp/server/auth.py
index b745d0b7..bb84d33d 100644
--- a/src/adcp/server/auth.py
+++ b/src/adcp/server/auth.py
@@ -223,6 +223,21 @@ class BearerTokenAuthMiddleware(BaseHTTPMiddleware):
     :param validate_token: Your token lookup. See :data:`TokenValidator`.
     :param unauthenticated_response: Optional override for the 401
         response body. Default is ``{"error": "unauthenticated"}``.
+    :param header_name: Which HTTP header carries the credential.
+        Default ``"authorization"`` (the spec-canonical bearer header).
+        Adopters with legacy clients sending tokens via a custom header
+        (e.g. ``"x-adcp-auth"``) override this. Header lookup is
+        case-insensitive (Starlette normalizes).
+    :param bearer_prefix_required: When ``True`` (default), the
+        middleware strips a ``"Bearer "`` prefix and rejects headers
+        without it. When ``False``, the raw header value is passed
+        verbatim to ``validate_token`` — appropriate for non-OAuth
+        custom-header schemes (``X-Api-Key: <token>``,
+        ``x-adcp-auth: <token>``, etc.). Adopters changing
+        ``header_name`` to a non-standard value usually want this set
+        to ``False``. **Security note:** setting this to ``False``
+        removes the prefix pre-filter; ``validate_token`` must be
+        defensive about unexpected input shapes and unbounded lengths.
     """
 
     def __init__(
@@ -231,10 +246,17 @@ def __init__(
         *,
         validate_token: TokenValidator,
         unauthenticated_response: dict[str, Any] | None = None,
+        header_name: str = "authorization",
+        bearer_prefix_required: bool = True,
     ) -> None:
         super().__init__(app)
         self._validate_token = validate_token
         self._unauth_body = unauthenticated_response or {"error": "unauthenticated"}
+        # Lower-cased once at construction so the per-request lookup
+        # avoids the normalization. Starlette's Headers does
+        # case-insensitive matching, so this is belt-and-suspenders.
+        self._header_name = header_name.lower()
+        self._bearer_prefix_required = bearer_prefix_required
 
     async def dispatch(self, request: Request, call_next: Any) -> Any:
         method, tool = await self._peek_jsonrpc(request)
@@ -249,7 +271,15 @@ async def dispatch(self, request: Request, call_next: Any) -> Any:
                 metadata_token = current_principal_metadata.set(None)
                 return await call_next(request)
 
-            bearer = _parse_bearer_header(request.headers.get("authorization", ""))
+            raw_header = request.headers.get(self._header_name, "")
+            if self._bearer_prefix_required:
+                bearer = _parse_bearer_header(raw_header)
+            else:
+                # Custom-header schemes (X-Api-Key, x-adcp-auth, etc.) —
+                # pass the raw value through unchanged. Strip whitespace
+                # since copy-paste tokens often pick up trailing newlines.
+                stripped = raw_header.strip()
+                bearer = stripped or None
             if not bearer:
                 return self._unauthenticated()
 
diff --git a/tests/test_auth_middleware.py b/tests/test_auth_middleware.py
index af83be6b..0d1c624f 100644
--- a/tests/test_auth_middleware.py
+++ b/tests/test_auth_middleware.py
@@ -569,3 +569,189 @@ def test_auth_context_factory_with_no_principal() -> None:
 # already boots the FastMCP initialize/tools-call flow end-to-end. The
 # tests in this file stay focused on the middleware class itself so
 # failures localise to the auth logic, not the transport plumbing.
+
+
+# ----- custom header / non-Bearer schemes ---------------------------------
+
+
+def _build_app_custom_header(
+    validator: Any, *, header_name: str, bearer_prefix_required: bool
+) -> Starlette:
+    app = Starlette(routes=[Route("/", _echo_handler, methods=["POST"])])
+    app.add_middleware(
+        BearerTokenAuthMiddleware,
+        validate_token=validator,
+        header_name=header_name,
+        bearer_prefix_required=bearer_prefix_required,
+    )
+    return app
+
+
+@pytest.mark.asyncio
+async def test_custom_header_x_adcp_auth_no_bearer_prefix() -> None:
+    """Salesagent-shaped scheme: ``x-adcp-auth: <raw-token>``.
+
+    The legacy salesagent server uses this header layout — no
+    ``Authorization`` header, no ``Bearer`` prefix. The middleware
+    must accept the raw token verbatim when ``bearer_prefix_required``
+    is False.
+    """
+    received_tokens: list[str] = []
+
+    def validator(token: str) -> Principal | None:
+        received_tokens.append(token)
+        return Principal(caller_identity="alice", tenant_id="acme")
+
+    app = _build_app_custom_header(
+        validator, header_name="x-adcp-auth", bearer_prefix_required=False
+    )
+    async with LifespanManager(app):
+        async with httpx.AsyncClient(
+            transport=httpx.ASGITransport(app=app), base_url="http://test"
+        ) as client:
+            resp = await client.post(
+                "/",
+                json={"method": "tools/call", "params": {"name": "get_products"}},
+                headers={"x-adcp-auth": "tok_alice_raw"},
+            )
+    assert resp.status_code == 200
+    assert received_tokens == ["tok_alice_raw"]  # passed through verbatim, no Bearer prefix
+
+
+@pytest.mark.asyncio
+async def test_custom_header_strips_whitespace() -> None:
+    """Trailing newlines / spaces (common in copy-pasted tokens) are stripped."""
+    received: list[str] = []
+
+    def validator(token: str) -> Principal | None:
+        received.append(token)
+        return Principal(caller_identity="alice")
+
+    app = _build_app_custom_header(validator, header_name="x-api-key", bearer_prefix_required=False)
+    async with LifespanManager(app):
+        async with httpx.AsyncClient(
+            transport=httpx.ASGITransport(app=app), base_url="http://test"
+        ) as client:
+            resp = await client.post(
+                "/",
+                json={"method": "tools/call", "params": {"name": "get_products"}},
+                headers={"x-api-key": "  tok_alice  "},
+            )
+    assert resp.status_code == 200
+    assert received == ["tok_alice"]
+
+
+@pytest.mark.asyncio
+async def test_custom_header_rejects_missing_credential() -> None:
+    """Custom-header mode still 401s when the configured header isn't present."""
+
+    def validator(token: str) -> Principal | None:
+        return Principal(caller_identity="alice")
+
+    app = _build_app_custom_header(
+        validator, header_name="x-adcp-auth", bearer_prefix_required=False
+    )
+    async with LifespanManager(app):
+        async with httpx.AsyncClient(
+            transport=httpx.ASGITransport(app=app), base_url="http://test"
+        ) as client:
+            # Send an Authorization header — but the middleware is configured
+            # to look at x-adcp-auth, so this must be rejected.
+            resp = await client.post(
+                "/",
+                json={"method": "tools/call", "params": {"name": "get_products"}},
+                headers={"authorization": "Bearer tok_alice"},
+            )
+    assert resp.status_code == 401
+
+
+@pytest.mark.asyncio
+async def test_custom_header_with_bearer_prefix_still_required() -> None:
+    """When ``bearer_prefix_required=True`` (the default), even a custom
+    header must carry the ``Bearer`` prefix. Useful for adopters using a
+    non-``Authorization`` header but keeping the OAuth2 envelope (e.g.
+    proxies that strip ``Authorization``)."""
+
+    def validator(token: str) -> Principal | None:
+        return Principal(caller_identity="alice")
+
+    app = _build_app_custom_header(
+        validator, header_name="x-proxied-auth", bearer_prefix_required=True
+    )
+    async with LifespanManager(app):
+        async with httpx.AsyncClient(
+            transport=httpx.ASGITransport(app=app), base_url="http://test"
+        ) as client:
+            # Without Bearer prefix → 401
+            resp1 = await client.post(
+                "/",
+                json={"method": "tools/call", "params": {"name": "get_products"}},
+                headers={"x-proxied-auth": "tok_alice"},
+            )
+            assert resp1.status_code == 401
+
+            # With Bearer prefix → 200
+            resp2 = await client.post(
+                "/",
+                json={"method": "tools/call", "params": {"name": "get_products"}},
+                headers={"x-proxied-auth": "Bearer tok_alice"},
+            )
+            assert resp2.status_code == 200
+
+
+@pytest.mark.asyncio
+async def test_custom_header_is_exclusive_no_fallback_to_authorization() -> None:
+    """Custom header_name is exclusive — Authorization is never consulted.
+
+    When both ``Authorization: Bearer X`` and ``x-adcp-auth: Y`` are
+    present and the middleware is configured for ``x-adcp-auth``, only
+    ``Y`` reaches the validator. There is no fallback to the standard
+    header. Closes the "I expected fallback to Authorization" footgun for
+    adopters who set header_name accidentally.
+    """
+    received: list[str] = []
+
+    def validator(token: str) -> Principal | None:
+        received.append(token)
+        return Principal(caller_identity="alice")
+
+    app = _build_app_custom_header(
+        validator, header_name="x-adcp-auth", bearer_prefix_required=False
+    )
+    async with LifespanManager(app):
+        async with httpx.AsyncClient(
+            transport=httpx.ASGITransport(app=app), base_url="http://test"
+        ) as client:
+            resp = await client.post(
+                "/",
+                json={"method": "tools/call", "params": {"name": "get_products"}},
+                headers={
+                    "Authorization": "Bearer tok_x",
+                    "x-adcp-auth": "tok_y",
+                },
+            )
+    assert resp.status_code == 200
+    assert received == ["tok_y"]  # x-adcp-auth wins; Authorization is ignored
+
+
+@pytest.mark.asyncio
+async def test_default_header_unchanged_for_existing_adopters() -> None:
+    """The defaults (``Authorization`` header + Bearer prefix) match the
+    pre-existing behavior. Existing adopters not setting the new params
+    see no behavioral change."""
+
+    def validator(token: str) -> Principal | None:
+        return Principal(caller_identity="alice")
+
+    # Use the original _build_app (no custom kwargs) — same as before.
+    app = _build_app(validator)
+    async with LifespanManager(app):
+        async with httpx.AsyncClient(
+            transport=httpx.ASGITransport(app=app), base_url="http://test"
+        ) as client:
+            resp = await client.post(
+                "/",
+                json={"method": "tools/call", "params": {"name": "get_products"}},
+                headers={"authorization": "Bearer tok_alice"},
+            )
+    assert resp.status_code == 200