SAML Metadata parsing does not correctly parse valid duration values.

No file or test is named in the report. Start by tracing SAML metadata handling for the cacheDuration attribute and the strconv.ParseInt error, then add coverage for the valid value PT5H. Done means valid SAML metadata using ISO 8601 duration syntax is accepted when adding an identity provider.

Bug report

• I confirm this is a bug with Supabase, not with my own application.
• I confirm I have searched the Docs, GitHub Discussions, and Discord.

Describe the bug

We have a customer that we are setting up with SAML authentication. Their metadata EntitiesDescriptor contains the following:

(Sanitized)
<md:EntitiesDescriptor xmlns:md="urn:oasis:names:tc:SAML:2.0:metadata" xmlns:ds="http://www.w3.org/2000/09/xmldsig#" xmlns:mdui="urn:oasis:names:tc:SAML:metadata:ui" xmlns:mdattr="urn:oasis:names:tc:SAML:metadata:attribute" xmlns:mdrpi="urn:oasis:names:tc:SAML:metadata:rpi" xmlns:shibmd="urn:mace:shibboleth:metadata:1.0" xmlns:xrd="http://docs.oasis-open.org/ns/xri/xrd-1.0" ....snip... validUntil="2024-08-09T23:11:46Z" cacheDuration="PT5H">

When adding this provider via supabase sso add we receive the following error:

Unexpected error adding identity provider: {"message":"Unexpected failure, please check server logs for more information"}

The server logs show:
(Sanitized)

{"component":"api","error":"strconv.ParseInt: parsing \"PT5H\": invalid syntax","level":"error","method":"POST","msg":"Unhandled server error: strconv.ParseInt: parsing \"PT5H\": invalid syntax","path":"/admin/sso/providers","referer":"https://<removed>","remote_addr":"3.95.37.194","request_id":"8abf1e44f73505f5-IAD","time":"2024-07-31T16:55:49Z"}

According to the spec:

https://docs.oasis-open.org/security/saml/v2.0/saml-schema-metadata-2.0.xsd

This is the cacheDuration schema:

<attribute name="cacheDuration" type="duration" use="optional"/>

According to the XML schema:

https://www.w3.org/TR/xmlschema-2/#duration

3.2.6.1 Lexical representation The lexical representation for duration is the [[ISO 8601]](https://www.w3.org/TR/xmlschema-2/#ISO8601) extended format PnYn MnDTnH nMnS, where nY represents the number of years, nM the number of months, nD the number of days, 'T' is the date/time separator, nH the number of hours, nM the number of minutes and nS the number of seconds. The number of seconds can include decimal digits to arbitrary precision.

This is a valid way of specifying a duration.

To Reproduce

1. Create an XML metadata file that uses Lexical representation to specify cacheDuration
2. Attempt to add this to an instance using supabase sso add
3. Get error

Expected behavior

Valid SAML metadata is processed successfully.