OAuth error oauth_problem=signature_invalid

Problem

When creating an application link, or using functionality that uses an application link, the applications aren't able to authenticate to each other.

The following appears in the application log:

oauth_problem=signature_invalid

Diagnosis

Environment

• Two applications are connected together using Application Links
• The authentication method used is OAuth

Cause

The Application URL of the link does not match the URL that the remote application is reporting. This can be caused by:

• The Base URL on the remote application is set to something other than the Application URL defined on the link
• A reverse proxy or port forwarding is configured, and the "Host" header is reporting the wrong host name or port
• A CDN or firewall might be removing GET parameters from the requests
• If you are using NGINX as the reverse proxy and using the proxy_cache  directive 
• The useBodyEncodingForURI tomcat parameter in the <confluence-install>/conf/server.xml is set to true

In this scenario, the affected applications will usually display other problems as well.

Resolution

Base URL

• Ensure the Base URL is correct for each application.

Application URL

• The Application URL should match the Base URL of the other application unless you're bypassing a reverse proxy.

• If the Application URL does not match the Base URL (and you're not bypassing a reverse proxy) then delete and recreate the Application Link.

Reverse Proxy

• If using a reverse proxy or port forwarding, ensure the application is correctly configured for use with a reverse proxy.

GET parameters removed

• Verify if CDN or firewall rules might be removing parameters from the requests. The request parameters should not be altered.

NGINX Reverse Proxy with  proxy_cache directive

NGINX caching rewrites HEAD requests to GET requests by default which will interfere with application link communication between Atlassian products.

• Workaround 1: Do not use the proxy_cache  directive in the Nginx configuration

• Workaround 2: If the proxy_cache  directive is required, then add this to the NGINX configuration which will allow caching to remain enabled without breaking OAuth communication:

  proxy_cache_convert_head   off;
  proxy_cache_key            $scheme$request_method$proxy_host$request_uri;

Tomcat

1. Look for the following part in <confluence-install>/conf/server.xml.

   <Connector port="8090" connectionTimeout="20000" redirectPort="8443"
    maxThreads="48" minSpareThreads="10"
    enableLookups="false" acceptCount="10" debug="0" URIEncoding="UTF-8"
    protocol="org.apache.coyote.http11.Http11NioProtocol" 
    useBodyEncodingForURI="true"/>

2. If the useBodyEncodingForURI is in the server.xml, remove the parameter or set it to false

   <Connector port="8090" connectionTimeout="20000" redirectPort="8443"
    maxThreads="48" minSpareThreads="10"
    enableLookups="false" acceptCount="10" debug="0" URIEncoding="UTF-8"
    protocol="org.apache.coyote.http11.Http11NioProtocol" 
    useBodyEncodingForURI="false"/>