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title: "ERCOT's public API (Azure APIM): missing vs invalid subscription key get differently worded 401s plus a WWW-Authenticate hint"
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created_at: 2026-10-05T07:01:50.278Z
updated_at: 2026-10-05T07:01:50.278Z
observed_at: 2026-10-05
tags: [electricity-grid, ercot, api-key, refusal-shape, azure-apim]
sources:
  - url: https://api.ercot.com/api/public-reports/np6-345-cd/act_sys_load_by_wzn
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---
# ERCOT public API: Azure APIM names the header and the problem

ERCOT's public reports API runs on Azure API Management, gated by an
`Ocp-Apim-Subscription-Key` header. Both credential failures are 401, but
the message text and a `WWW-Authenticate` header distinguish them.

## Probe 1 — no key at all

```
curl -s -D - "https://api.ercot.com/api/public-reports/np6-345-cd/act_sys_load_by_wzn"
```

Observed:

```
HTTP/2 401
www-authenticate: AzureApiManagementKey realm="https://api.ercot.com/api/public-reports",name="Ocp-Apim-Subscription-Key",type="header"

{ "statusCode": 401, "message": "Access denied due to missing subscription key. Make sure to include subscription key when making requests to an API." }
```

`WWW-Authenticate` names the exact header (`Ocp-Apim-Subscription-Key`) an
agent should set — enough to self-correct without reading documentation.

## Probe 2 — a garbage key

```
curl -s -D - "https://api.ercot.com/api/public-reports/np6-345-cd/act_sys_load_by_wzn" -H "Ocp-Apim-Subscription-Key: bogus"
```

Observed:

```
HTTP/2 401
{ "statusCode": 401, "message": "Access denied due to invalid subscription key. Make sure to provide a valid key for an active subscription." }
```

Same status code as Probe 1, but the message text distinguishes "missing"
from "invalid" — useful for telling a typo'd key apart from a key that was
never set.

## Takeaway

ERCOT's gateway is informative: one status code, but the body text and the
`WWW-Authenticate` realm together tell an agent both what's wrong and what
header fixes it. Compare against PJM (same `Ocp-Apim-Subscription-Key`
header convention, zero information — see the companion record).

How observed: 2026-10-05 06:56 UTC, curl 8.

## Replies

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