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Why Jenkins returns 403 for a cURL POST
A 403 is not enough to identify the cause. Jenkins may return it when the client omits preemptive authentication, a password-authenticated POST lacks valid CSRF protection, or the authenticated user lacks permission for the requested operation. Jenkins documents that it does not negotiate authentication: it can return 403 immediately, so send credentials with the initial request. See the Jenkins Project’s Authenticating scripted clients and CSRF Protection documentation.
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Authentication establishes who the user is; authorization determines what that user may do on the target object. A successful login, or a successful GET, does not prove the user can update project security. Jenkins checks the permission required for the requested operation against the configured authorization strategy. The Jenkins Project explains this distinction in its Access Control documentation.
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Try the API-token POST first
For scripted requests, Jenkins recommends using a user’s API token in place of the password. API-token-authenticated requests are exempt from Jenkins CSRF crumb protection, so this avoids the crumb-and-cookie exchange. The token does not grant extra permissions: the account still needs the permission for the operation on the target job or project.
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curl -u 'USER:API_TOKEN'
-X POST
'https://jenkins.example.com/job/JOB/build'Replace the example host, user, token, and job path with your values. For a job in a folder, include the folder path in Jenkins’ URL format, such as /job/FOLDER/job/JOB/; URL-encode names containing characters that have special meaning in a URL. Use your actual Jenkins root URL, including any context path, rather than assuming Jenkins is installed at the domain root.
For a project-security or configuration change, use the POST endpoint appropriate to that operation; the build endpoint above is only an example. A successful POST to one endpoint does not establish that the user is authorized for another.
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If you use a password, send the crumb and cookie together
Jenkins POST requests generally require a crumb when authenticated with a username and password. Request the crumb first while saving the response cookie, then send the returned crumb request-field header and that same cookie with the POST. A crumb without its associated session cookie may be rejected.
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The following example uses jq to read the JSON fields returned by Jenkins’ crumb issuer:
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curl -u 'USER:PASSWORD'
-c cookies.txt
'https://jenkins.example.com/crumbIssuer/api/json'
-o crumb.json
CRUMB_HEADER=$(jq -r '.crumbRequestField + ":" + .crumb' crumb.json)
curl -u 'USER:PASSWORD'
-b cookies.txt
-H "$CRUMB_HEADER"
-X POST
'https://jenkins.example.com/job/JOB/build'Keep the root URL, credentials, and target path consistent across both requests. Treat the cookie file, crumb response, and credentials as sensitive; remove temporary files when finished. If the crumb request itself returns an error, resolve its URL, authentication, or proxy issue before retrying the POST. Jenkins’ CSRF documentation describes the crumb issuer API and the need to send the crumb with the cookie.
Choose the fix that matches the request
| Authentication method | CSRF handling | What it does not solve |
|---|---|---|
| Username and API token using Basic authentication | Jenkins exempts API-token-authenticated requests from crumb protection. | Missing permission, incorrect endpoint, or wrong job path. |
| Username and password using Basic authentication | Fetch a crumb and retain the matching session cookie; send both with the POST. | Missing permission, incorrect endpoint, or wrong job path. |
Check the URL and authentication before changing permissions
- Verify the Jenkins root URL. Use the same scheme, host, port, and any configured context path that you use to reach Jenkins. Account for a reverse proxy if it changes the public URL.
- Check the target with a harmless authenticated GET. Request a page or API endpoint for the intended job using the same user and API token. Confirm that the response identifies the expected Jenkins instance and job rather than a login page, proxy response, or different path.
- Send credentials on the first request. Use
curl -u 'USER:API_TOKEN'rather than relying on an authentication challenge. Jenkins documents that scripted clients should use preemptive authentication. - Verify folder and job names. Nested jobs require the correct repeated
/job/NAMEpath segments. Encode reserved characters in names. A 404 more often points to a wrong URL or path than to a permission problem. - Account for the proxy and crumb issuer. A reverse proxy or plugin-provided crumb issuer can affect the reachable URL or crumb flow. Ensure the crumb request and POST go through the intended Jenkins address and preserve the session cookie.
Confirm the exact permission for project security
Once the endpoint and authentication are sound, check the permission required by the specific action. Jenkins authorization strategies can grant access globally or, with Matrix-based or Project-based Matrix Authorization Strategy, at the project level. Whether a project can use its own access-control list depends on the configured strategy.
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Ask a Jenkins administrator to inspect the effective permissions for the account on the target job or project, including inherited or global grants where applicable. Do not assume that permission to view or build a job includes permission to configure it or change its security settings. The necessary permission depends on the operation and authorization configuration; there is no single permission rule that applies to every Jenkins installation.
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- 403 on the crumb request: Check whether credentials are sent preemptively, the user is valid, and the crumb issuer URL is correct. Review Jenkins or proxy logs if the response remains unclear.
- 403 on the POST with password authentication: Confirm that the crumb header came from the current crumb response and that the POST reuses the corresponding cookie file. Alternatively, use an API token.
- 403 on the POST with an API token: Crumb handling is not the likely blocker for an API-token-authenticated request. Check that the token belongs to the intended user and that the user has the permission required for that action on that project.
- 404: Recheck the Jenkins root URL, context path, folder/job segments, endpoint, and URL encoding.
- Unexpected redirects or HTML instead of the expected response: Check whether the request is reaching the right Jenkins instance through the proxy and whether the URL points to the expected endpoint.
Inspect the HTTP status and Jenkins logs for the relevant request. Do not disable CSRF protection to make a script work: Jenkins recommends keeping it enabled, including on private trusted networks. Fix the request’s authentication and crumb handling instead.
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