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Authenticate to a document-generation API using the method its provider supports. For server-to-server integrations, OAuth 2.0 access tokens are a common option; some APIs instead require a provider-issued API key. Whichever you use, keep credentials on the server, send them only over validated HTTPS, request only the access needed, and keep authentication separate from permissions to use templates, data, and generated files.
How do I authenticate to a document generation API?
Start with the API provider’s current documentation—not with a preferred authentication technique. Record the API version and environment, how credentials are issued, the required request format, supported permissions, and how credentials can be rotated or revoked. There is no single authentication contract shared by all document APIs.
For a typical server-to-server integration, the provider may issue an OAuth 2.0 access token, which your server sends in the HTTP Authorization header. Another provider may require a static API key. Use the documented mechanism and header format exactly; do not assume an API accepts OAuth, or that an API key can substitute for an OAuth token.
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- Check the API contract. Note the required authentication scheme, token or key audience, supported scopes, and any provider-specific issuance and renewal steps.
- Store the credential server-side. Use a controlled secret-management system or equivalent; do not put confidential credentials in browser code or mobile application bundles.
- Send credentials over validated TLS. For a bearer token, use
Authorization: Bearer <token>. Do not include it in a URL or query string. - Authorize each operation. Limit what the caller can do with templates, customer records, document inputs, and generated files, even after its identity has been authenticated.
API key or OAuth: which should I use?
Use the provider’s supported option. These approaches have different operating characteristics, but neither is automatically available for every document-generation API. OAuth bearer tokens are standardized for API access; a static key can be straightforward when the provider explicitly documents it. This guidance does not establish how any particular document vendor issues, scopes, expires, or revokes its keys.
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| Method | What it means for your integration | Questions to verify |
|---|---|---|
| Provider-issued API key or static secret | A credential your service presents as the API requires. Treat it as a long-lived secret unless the provider documents an expiry or rotation mechanism. | Where does the provider expect it? Can it be restricted or revoked? How do you rotate it without interrupting document generation? |
| OAuth bearer access token | A party holding the token can use it as the client within the token’s effective permissions. OAuth can support expiry and access controls, but the provider’s implementation determines the available controls. | How is the token obtained and renewed? What audience and scopes are accepted? What are the expiry, storage, and revocation behaviors? |
| OAuth with mTLS or DPoP sender constraint | Additional proof binds use of an access token to a client-held certificate or key, which can reduce the usefulness of a stolen token if the proof material remains protected. | Does the API and your client stack support the mechanism? How will you protect, rotate, and recover the certificate or key? |
OAuth does not make an access token harmless if it leaks. RFC 6750 defines a bearer token as usable by any party in possession of it, without proving possession of a cryptographic key. Treat bearer tokens accordingly: possession is effectively authority to act within the access the token grants.
How should I send and store an API token?
Use the Authorization header over HTTPS
RFC 6750 requires TLS for bearer-token use and calls for certificate-chain validation. Send a token in the documented authorization header, commonly Authorization: Bearer <access-token>, and use a client that validates the server certificate chain. Never place a token in a query string, URL, or page address: URLs can be retained in logs and other records.
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Keep confidential credentials out of clients and logs
Keep client secrets, private keys, API keys, and access tokens in a server-side secrets store or similarly controlled system. A browser or mobile application bundle cannot reliably keep a confidential credential secret from its users. Configure logs, traces, error reporting, and support workflows to redact authorization headers, secrets, signed assertions, and document payloads that contain sensitive data.
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Where the API supports them, request only the scopes needed and the intended audience. Appropriately short token lifetimes can reduce how long a leaked bearer token remains useful; they do not replace secure storage or revocation planning. Rotate credentials according to provider support and organizational policy. Test rotation and revocation in a non-production environment before relying on them in production.
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- FAST & CONVENIENT LOGIN: Plug in your YubiKey 5 NFC via USB and tap it, or tap it against your phone (NFC), to authenticate. No batteries, no internet connection, and no extra fees required
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What does a secure API request look like?
The following is a generic bearer-token request pattern, not a document vendor’s exact endpoint or schema. The provider determines the document-generation URL, request method, payload, token acquisition flow, and accepted permissions. Set DOCUMENT_API_URL to the documented operation URL, ACCESS_TOKEN to a valid token obtained through that provider’s documented flow, and DOCUMENT_JSON to its accepted request body before running a sample. Do not place real credentials or sensitive document data in shell history or shared logs.
cURL
curl --fail-with-body
--header "Authorization: Bearer ${ACCESS_TOKEN}"
--header "Content-Type: application/json"
--data "${DOCUMENT_JSON}"
"${DOCUMENT_API_URL}"Python
import os
import requests
response = requests.post(
os.environ["DOCUMENT_API_URL"],
headers={
"Authorization": f"Bearer {os.environ['ACCESS_TOKEN']}",
"Content-Type": "application/json",
},
data=os.environ["DOCUMENT_JSON"],
timeout=30,
)
response.raise_for_status()
print(response.status_code)Node.js
const res = await fetch(process.env.DOCUMENT_API_URL, {
method: 'POST',
headers: {
Authorization: `Bearer ${process.env.ACCESS_TOKEN}`,
'Content-Type': 'application/json',
},
body: process.env.DOCUMENT_JSON,
});
if (!res.ok) {
throw new Error(`Document API returned HTTP ${res.status}`);
}These samples intentionally do not invent a token endpoint, grant type, scope name, request schema, or vendor URL. Obtain and refresh the token according to the selected provider’s instructions; do not assume the client-credentials grant is appropriate for a user-facing or delegated authorization flow.
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When should I add mTLS or DPoP?
Consider sender-constrained tokens when a stolen or leaked access token would create significant exposure and both the API provider and your client stack support the mechanism. Mutual TLS (mTLS) uses a client certificate; Demonstrating Proof of Possession (DPoP) uses key-based proof. RFC 9700, the OAuth 2.0 Security Best Current Practice published in January 2025, recommends sender-constraining access tokens, including with mTLS or DPoP, to help prevent misuse of stolen or leaked tokens.
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These options add operational responsibilities rather than removing them. Plan how private keys or certificates are stored, deployed, rotated, and recovered; test what happens when proof material expires or is unavailable. Avoid adopting a mechanism your provider does not implement or your team cannot operate reliably.
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- FAST & CONVENIENT LOGIN: Plug in your Security Key C NFC via USB-C and tap it, or tap it against your phone (NFC) to authenticate. No batteries, no internet connection, and no extra fees required.
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Authentication is not document authorization
Authentication establishes that the API recognizes a caller. Authorization determines what that caller may do. A valid token should not automatically grant access to every template, customer record, document input, or generated file. Apply operation- and object-level checks, including when a caller supplies a template identifier or requests a document by ID. Limit credentials and token permissions where supported, and enforce application-level access rules for each resource.
Troubleshooting authentication failures
- 401 Unauthorized: Check that the credential is present, unexpired, correctly formatted, and issued for the API environment you are calling. Confirm the scheme and header name against the provider’s docs.
- 403 Forbidden: The credential may be recognized but lack permission for the operation or resource. Verify supported scopes, audience, account access, and resource-level authorization.
- Works in test, fails in production: Confirm that the production endpoint uses production credentials and that the credential is configured for that environment. Do not copy test secrets into production by default.
- Intermittent failures after deployment: Check token expiry and renewal, synchronized clocks where relevant, and whether all application instances received the current credential during rotation.
- Unexpected credential exposure: Revoke or rotate the affected credential using the provider’s supported process, review relevant access records, and remove the secret from logs, tickets, or repositories where possible. Redaction reduces future exposure but does not make an already disclosed token safe.
- mTLS or DPoP requests fail: Check provider support, certificate or key configuration, proof generation, and rotation state. Keep a tested recovery procedure for unavailable or expired proof material.
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ScreenshotNeo is a separate website screenshot API and MCP server, not a document-generation API. If your task is to capture a web page rather than generate a document, one GET request can return an image or PDF. Its access key is still a credential: follow ScreenshotNeo’s documented handling guidance and keep it out of public client code.
ScreenshotNeo API documentation
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpPython: import requests; r = requests.get("https://api.screenshotneo.com/v1/shot", params={"access_key": "YOUR_API_KEY", "url": "https://stripe.com"}, timeout=90); open("shot.webp", "wb").write(r.content)
Node.js: const q = new URLSearchParams({ access_key: 'YOUR_API_KEY', url: 'https://stripe.com' }); const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);
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