What authentication methods does OSB support for outbound Proxy Server authentication?
The OSB Administrators Guide has this to say about connecting to Business Services through an HTTP proxy server.
36.7.4 Using Proxy Servers
You can configure business services to route messages through a proxy server. You do this by creating a proxy server resource that specifies one or more proxy servers together with the necessary credentials. You can then associate this proxy server resource with a business service. This instructs Oracle Service Bus to connect to the business service through the configured proxy server.
Adding multiple proxy servers to a resource enables Oracle Service Bus to perform load balancing and offer fault tolerance among the configured proxy servers. The credentials are used when opening a connection to the proxy server. If a particular proxy server is not reachable, Oracle Service Bus attempts to use the next proxy server in the configuration. If all proxy servers are unreachable, Oracle Service Bus tries to connect to the back end service directly. If that too fails, a fault is raised and sent back to the caller