# 🧾 Environment Variables and `ccptaskid`

This page documents special **environment variables** made available during method execution.  
These allow your code to uniquely identify each replica, manage security tokens, and interact with D4Science services.

---

## 🔀 `ccptaskid`: Execution Replica Identifier

When a method is executed in parallel (e.g. multiple inputs or parallel containers), each instance is assigned a unique `ccptaskid`.

You can use this to **generate replica-specific outputs**:

```bash
mkdir -p /ccp_data/output
echo $RANDOM > /ccp_data/output/$(printenv ccptaskid).txt
```

This ensures files don’t overwrite each other across replicas.

---

## 🔐 Auth Environment Variables

When your method runs, the container receives the following secure environment variables:

| Variable         | Description                                  |
|------------------|----------------------------------------------|
| `ccpiamurl`      | IAM server URL                               |
| `ccpclientid`    | Client ID for token operations                |
| `ccprefreshtoken`| Refresh token for authentication             |
| `ccpcontext`     | VRE/Context in which the method runs         |

---

## 🔄 Renewing Tokens from Inside the Method

You can use these variables to request a **login token** and an **UMA access token**  
for accessing secured services like the Workspace or Catalogue.

---

### 🐍 Example: Token Renewal in Python

```python
import os, requests

# Get auth info
refreshtoken = os.environ["ccprefreshtoken"]
context = os.environ["ccpcontext"]
clientid = os.environ["ccpclientid"]
iam = os.environ["ccpiamurl"]

# Login request
logindata = {
  'grant_type': 'refresh_token',
  'client_id': clientid,
  'refresh_token': refreshtoken
}
loginheaders = {
  "Accept": "application/json",
  "Content-Type": "application/x-www-form-urlencoded"
}

# UMA token request
umadata = {
  'grant_type': 'urn:ietf:params:oauth:grant-type:uma-ticket',
  'audience': context
}
umaheaders = {
  "Accept": "application/json",
  "Content-Type": "application/x-www-form-urlencoded"
}

def getToken():
    resp1 = requests.post(iam, data=logindata, headers=loginheaders)
    jwt = resp1.json()
    umaheaders["Authorization"] = "Bearer " + jwt["access_token"]
    resp2 = requests.post(iam, data=umadata, headers=umaheaders)
    return resp2.json()["access_token"]

# Use token
token = getToken()
headers = {"Authorization": f"Bearer {token}", "Accept": "application/json"}
vrefolder = requests.get("https://workspace.d4science.org/vrefolder", headers=headers).json()
```

---

## 🔗 Related Pages

- 🔐 [Credentials input](/04_methods_development/05_input_types/05_input_credentials.md)

- 📦 [Runtime architecture](/05_advanced_topics/01_architecture/02_runtime_architecture.md)

- 🧱 [Method scripts and placeholders](/04_methods_development/06_scripts_and_placeholders.md)