feat(ask_sb): Add headers param to config to allow users to specify custom headers (#449)

Author: brendan-kellam

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Added multi-branch indexing support for Gerrit. [#433](https://github.com/sourcebot-dev/sourcebot/pull/433)
 - [ask sb] Added `reasoningEffort` option to OpenAI provider. [#446](https://github.com/sourcebot-dev/sourcebot/pull/446)
+- [ask db] Added `headers` option to all providers. [#449](https://github.com/sourcebot-dev/sourcebot/pull/449)
 
 ### Fixed
 - Removed prefix from structured log output. [#443](https://github.com/sourcebot-dev/sourcebot/pull/443)

docs/docs/configuration/language-model-providers.mdx

@@ -324,8 +324,34 @@ The OpenAI compatible provider allows you to use any model that is compatible wi
 }
 ```
 
+# Custom headers
 
-## Schema reference
+You can pass custom headers to the language model provider by using the `headers` parameter. Header values can either be a string or a environment variable. Headers are supported for all providers.
+
+```json wrap icon="code" Example config with custom headers
+{
+    "$schema": "https://raw.githubusercontent.com/sourcebot-dev/sourcebot/main/schemas/v3/index.json",
+    "models": [
+        {
+            // ... provider, model, displayName, etc...
+
+            // Key-value pairs of headers
+            "headers": {
+                // Header values can be passed as a environment variable...
+                "my-secret-header": {
+                    "env": "MY_SECRET_HEADER_ENV_VAR"
+                },
+
+                // ... or directly as a string.
+                "my-non-secret-header": "plaintextvalue"
+            }
+        }
+    ]
+}
+```
+
+
+# Schema reference
 
 <Accordion title="Reference">
 [schemas/v3/languageModel.json](https://github.com/sourcebot-dev/sourcebot/blob/main/schemas/v3/languageModel.json)