adding support for openai api base

.env.example

@@ -1,5 +1,6 @@
 # OpenAI
 OPENAI_API_KEY = ""
+OPENAI_API_BASE = ""
 # Cohere
 COHERE_API_KEY = ""
 # OpenRouter

docs/my-website/docs/completion/supported.md

@@ -17,6 +17,8 @@ liteLLM reads key naming, all keys should be named in the following format:
 | gpt-3.5-turbo-16k-0613    | `completion('gpt-3.5-turbo-16k-0613', messages)` | `os.environ['OPENAI_API_KEY']`       |
 | gpt-4            | `completion('gpt-4', messages)`         | `os.environ['OPENAI_API_KEY']`       |
 
+These also support the `OPENAI_API_BASE` environment variable, which can be used to specify a custom API endpoint.
+
 ### Azure OpenAI Chat Completion Models
 
 | Model Name       | Function Call                           | Required OS Variables                     |

litellm/main.py

@@ -211,11 +211,9 @@ def completion(
             openai.api_type = "openai"
             # note: if a user sets a custom base - we should ensure this works
             api_base = (
-                custom_api_base if custom_api_base is not None else litellm.api_base
-            )  # allow for the setting of dynamic and stateful api-bases
-            openai.api_base = (
-                api_base if api_base is not None else "https://api.openai.com/v1"
+                custom_api_base or litellm.api_base or get_secret("OPENAI_API_BASE")
             )
+            openai.api_base = api_base or "https://api.openai.com/v1"
             openai.api_version = None
             if litellm.organization:
                 openai.organization = litellm.organization