# Environment Variables

The HTTPX library can be configured via environment variables.
Environment variables are used by default. To ignore environment variables, `trust_env` has to be set `False`. There are two ways to set `trust_env` to disable environment variables:

* On the client via `httpx.Client(trust_env=False)`.
* Using the top-level API, such as `httpx.get("<url>", trust_env=False)`.

Here is a list of environment variables that HTTPX recognizes and what function they serve:

## `SSLKEYLOGFILE`

Valid values: a filename

If this environment variable is set, TLS keys will be appended to the specified file, creating it if it doesn't exist, whenever key material is generated or received. The keylog file is designed for debugging purposes only.

Support for `SSLKEYLOGFILE` requires Python 3.8 and OpenSSL 1.1.1 or newer.

Example:

```python
# test_script.py
import httpx

with httpx.AsyncClient() as client:
    r = client.get("https://google.com")
```

```console
SSLKEYLOGFILE=test.log python test_script.py
cat test.log
# TLS secrets log file, generated by OpenSSL / Python
SERVER_HANDSHAKE_TRAFFIC_SECRET XXXX
EXPORTER_SECRET XXXX
SERVER_TRAFFIC_SECRET_0 XXXX
CLIENT_HANDSHAKE_TRAFFIC_SECRET XXXX
CLIENT_TRAFFIC_SECRET_0 XXXX
SERVER_HANDSHAKE_TRAFFIC_SECRET XXXX
EXPORTER_SECRET XXXX
SERVER_TRAFFIC_SECRET_0 XXXX
CLIENT_HANDSHAKE_TRAFFIC_SECRET XXXX
CLIENT_TRAFFIC_SECRET_0 XXXX
```

## `SSL_CERT_FILE`

Valid values: a filename

If this environment variable is set then HTTPX will load
CA certificate from the specified file instead of the default
location.

Example:

```console
SSL_CERT_FILE=/path/to/ca-certs/ca-bundle.crt python -c "import httpx; httpx.get('https://example.com')"
```

## `SSL_CERT_DIR`

Valid values: a directory following an [OpenSSL specific layout](https://www.openssl.org/docs/manmaster/man3/SSL_CTX_load_verify_locations.html).

If this environment variable is set and the directory follows an [OpenSSL specific layout](https://www.openssl.org/docs/manmaster/man3/SSL_CTX_load_verify_locations.html) (ie. you ran `c_rehash`) then HTTPX will load CA certificates from this directory instead of the default location.

Example:

```console
SSL_CERT_DIR=/path/to/ca-certs/ python -c "import httpx; httpx.get('https://example.com')"
```

## Proxies

The environment variables documented below are used as a convention by various HTTP tooling, including:

* [cURL](https://github.com/curl/curl/blob/master/docs/MANUAL.md#environment-variables)
* [requests](https://github.com/psf/requests/blob/master/docs/user/advanced.rst#proxies)

For more information on using proxies in HTTPX, see [HTTP Proxying](advanced.md#http-proxying).

### `HTTP_PROXY`, `HTTPS_PROXY`, `ALL_PROXY`

Valid values: A URL to a proxy

`HTTP_PROXY`, `HTTPS_PROXY`, `ALL_PROXY` set the proxy to be used for `http`, `https`, or all requests respectively.

```bash
export HTTP_PROXY=http://my-external-proxy.com:1234

# This request will be sent through the proxy
python -c "import httpx; httpx.get('http://example.com')"

# This request will be sent directly, as we set `trust_env=False`
python -c "import httpx; httpx.get('http://example.com', trust_env=False)"

```

### `NO_PROXY`

Valid values: a comma-separated list of hostnames/urls

`NO_PROXY` disables the proxy for specific urls

```bash
export HTTP_PROXY=http://my-external-proxy.com:1234
export NO_PROXY=http://127.0.0.1,python-httpx.org

# As in the previous example, this request will be sent through the proxy
python -c "import httpx; httpx.get('http://example.com')"

# These requests will be sent directly, bypassing the proxy
python -c "import httpx; httpx.get('http://127.0.0.1:5000/my-api')"
python -c "import httpx; httpx.get('https://www.python-httpx.org')"
```