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This page introduces important policy and procedures associated with InCommon metadata. Other pages outline describe the availability of multiple metadata aggregates and provide guidance on how to configure specific metadata clients. General configuration issues, including the configuration of outbound firewalls, are discussed below.

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Info

It is strongly recommended that InCommon SPs and IdPs refresh and verify metadata at least daily. An optimal configuration would attempt to refresh metadata every hour, (assuming your client supports HTTP Conditional GET).

Participants are strongly encouraged to use SAML metadata client software that properly handles metadata; failure to do so can have profound effects on the successful use of the Federation. In addition to maintaining the security of your own deployment, proper metadata use is critical to ensure that other participants can depend on your system behaving correctly when they make changes.

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In addition, if you don't refresh your metadata regularly, it is likely that a software implementation will fail at some point since the XML document carries an expiration date (validUntil) that causes the metadata to expire in approximately two weeks. InCommon strongly recommends that you do not rely on the actual length of this validity interval in any way, and in fact, we reserve the right to shorten the validity interval with little or no notice.

Metadata Refresh Process

The mechanics of Here are the steps to deploy a secure, automated metadata refresh process:

  1. Choose the right metadata aggregate for your particular deploymentDeploy and configure an automated metadata refresh process:
  2. Configure your metadata client
  3. Verify the XML signature on downloaded metadata
  4. Validate the expiration date on downloaded metadata
    5. Adjust your outbound firewall rulesone of three Metadata Aggregates
  5. Obtain an authentic copy of the Metadata Signing Certificate
  6. Install and configure recommended Metadata Client Software:
    1. Refresh metadata at least daily (but more often if possible)
    2. Validate the expiration date on downloaded metadata
    3. Verify the XML signature on downloaded metadata
  7. Adjust your outbound firewall rules (if necessary)

Refresh Interval

Deployments are strongly encouraged to refresh metadata at least daily. If your metadata client supports HTTP Conditional GET, configure the client to refresh metadata every hour. This strategy provides the best protection in the event of a key compromise.

Validity Check

Federation metadata has an expiration date, much like an X.509 certificate. It is important that expired metadata not be accepted, otherwise an attacker would be able to substitute expired metadata in conjunction with metadata refresh. In particular, a metadata file should not be accepted if any of the following conditions are true:

  1. If the metadata file does not have a validUntil XML attribute on the root element.
  2. If the validUntil date on the root element is expired.
  3. If the validUntil date on the root element is too far into the future.

A metadata refresh process should check each of the above conditions before accepting the metadata. Alternatively, if your SAML implementation is known to ignore/reject expired metadata (a basic correctness requirement), it may be sufficient to ensure that a validUntil attribute exists and its date value is not unexpectedly far into the future.

Warning
titleValidate the expiration date on InCommon metadata!

Verifying the signature on a SAML metadata file does not validate the presence or value of an expiration date. The only way to validate the expiration date is to parse the XML.

Signature Verification

Federation metadata is signed for integrity and authenticity. Participants are strongly encouraged to verify the XML signature on the metadata file before use; failure to do so will seriously compromise the security of your SAML deployment.

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The InCommon Federation is based on the Explicit Key Trust Model, one of several possible metadata trust models. To bootstrap the trust fabric of the Federation, participants download and configure an authentic copy of the metadata verification certificate Metadata Signing Certificate into their metadata refresh process. The certificate must be obtained securely since all subsequent operations depend on it.

Once the certificate file is locally installed, you can use it to verify the signature on the metadata file. For example, you could use the XmlSecTool (or some similar 3rd-party tool) to verify the signature:

Code Block
languagebash

$ /usr/bin/curl --silent --remote-name $ MD_LOCATION=http://md.incommon.org/InCommon/InCommon-metadata.xml
$ MD_PATH=/tmp/InCommon-metadata.xml
$ /usr/bin/curl --silent $MD_LOCATION > $MD_PATH
$ ./xmlsectool.sh --verifySignature --signatureRequired \
    --certificate $CERT$MD_CERT_PATH --inFile $MD_PATH
INFO  XmlSecTool - Reading XML document from file '/tmp/InCommon-metadata.xml'
INFO  XmlSecTool - XML document parsed and is well-formed.
INFO  XmlSecTool - XML document signature verified.

You may also want to schema validate the metadata:

Code Block
languagebash

$ ./xmlsectool.sh --validateSchema \
    --schemaDirectory schema-files$SCHEMA_DIR --inFile $MD_PATH
INFO  XmlSecTool - Reading XML document from file '/tmp/InCommon-metadata.xml'
INFO  XmlSecTool - XML document parsed and is well-formed.
INFO  XmlSecTool - XML document is schema valid

For convenience, we provide a set of (suitably modified) schema files that permit offline schema validation.

Expiry Verification

Federation metadata has an expiration date, much like an X.509 certificate. It is important that expired metadata not be accepted, otherwise an attacker would be able to substitute expired metadata in conjunction with a metadata refresh. In particular, a metadata file should not be accepted if either of the following conditions are true:

  1. If the metadata file does not have a validUntil attribute on the root element.
  2. If the validUntil attribute on the root element is expired.

A metadata reload process should check each of the above conditions before accepting the metadata; alternatively if your SAML implementation is known to ignore/reject expired metadata (a basic correctness requirement), it may be sufficient to ensure that a validUntil attribute exists and is not unexpectedly far into the future.

Warning
titleVerify the expiration date independently!

Verifying the signature on a SAML metadata file does not verify the presence or value of an expiration date. The only way to verify the expiration date is to parse the XML.

Anchor
firewall-config
firewall-config

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Depending on your environment, you may have to poke a hole in an outbound firewall to allow your metadata client to reach the metadata server. In that case, you will actually want to poke two holes in that firewall since there are two metadata physical servers as described below.

Hostname md.incommon.org resolves to one of two identical servers, either in Michigan (207.75.165.125) or Indiana (140.182.44.53). The actual server used at any given point in time is unspecified and left to the discretion of InCommon Operations. If one of the servers goes down or requires maintenance, the other can be brought up within minutes, with minimal disruption of services.

Therefore, please make sure both your SAML implementation and your metadata refresh processes are configured with hostname md.incommon.org (as opposed to an IP address). On the other hand, make sure your outbound firewall (if any) is configured with both IP addresses (207.75.165.125 and 140.182.44.53).on the Metadata Server wiki page.

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