feat: support setting headers via env

Author: stainless-app[bot]

src/lithic/_client.py

@@ -22,7 +22,11 @@
     RequestOptions,
     not_given,
 )
-from ._utils import is_given, get_async_library
+from ._utils import (
+    is_given,
+    is_mapping_t,
+    get_async_library,
+)
 from ._compat import cached_property
 from ._version import __version__
 from ._response import to_streamed_response_wrapper, async_to_streamed_response_wrapper
@@ -197,6 +201,15 @@ def __init__(
             except KeyError as exc:
                 raise ValueError(f"Unknown environment: {environment}") from exc
 
+        custom_headers_env = os.environ.get("LITHIC_CUSTOM_HEADERS")
+        if custom_headers_env is not None:
+            parsed: dict[str, str] = {}
+            for line in custom_headers_env.split("\n"):
+                colon = line.find(":")
+                if colon >= 0:
+                    parsed[line[:colon].strip()] = line[colon + 1 :].strip()
+            default_headers = {**parsed, **(default_headers if is_mapping_t(default_headers) else {})}
+
         super().__init__(
             version=__version__,
             base_url=base_url,
@@ -612,6 +625,15 @@ def __init__(
             except KeyError as exc:
                 raise ValueError(f"Unknown environment: {environment}") from exc
 
+        custom_headers_env = os.environ.get("LITHIC_CUSTOM_HEADERS")
+        if custom_headers_env is not None:
+            parsed: dict[str, str] = {}
+            for line in custom_headers_env.split("\n"):
+                colon = line.find(":")
+                if colon >= 0:
+                    parsed[line[:colon].strip()] = line[colon + 1 :].strip()
+            default_headers = {**parsed, **(default_headers if is_mapping_t(default_headers) else {})}
+
         super().__init__(
             version=__version__,
             base_url=base_url,