feat: support setting headers via env

Author: stainless-app[bot]

src/steel/_client.py

@@ -26,6 +26,7 @@
 )
 from ._utils import (
     is_given,
+    is_mapping_t,
     maybe_transform,
     get_async_library,
     async_maybe_transform,
@@ -101,6 +102,15 @@ def __init__(
         if base_url is None:
             base_url = f"https://api.steel.dev"
 
+        custom_headers_env = os.environ.get("STEEL_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,
@@ -466,6 +476,15 @@ def __init__(
         if base_url is None:
             base_url = f"https://api.steel.dev"
 
+        custom_headers_env = os.environ.get("STEEL_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,