OIDC: this user can't understand how to generate sub claim

[Francesco Malvezzi]

hi all,

I'm a bit lost making sense of this error:

2022-08-29 14:13:02,147 - DEBUG 
[net.shibboleth.idp.plugin.oidc.op.profile.logic.AttributeResolutionSubjectLookupFunction:140] 
- Searching for 'sub' claim among encodeable attributes
2022-08-29 14:13:02,147 - WARN 
[net.shibboleth.idp.plugin.oidc.op.profile.logic.AttributeResolutionSubjectLookupFunction:182] 
- Unable to produce a viable 'sub' claim
2022-08-29 14:13:02,148 - ERROR 
[net.shibboleth.idp.plugin.oidc.op.profile.impl.SetSubjectToResponseContext:86] 
- Profile Action SetSubjectToResponseContext: Subject may not be null

The sub definition(s) is in the 
conf/examples/oidc-attribute-resolver.xml file: the

<AttributeDefinition id="subject" xsi:type="Scoped" scope="%{idp.scope}"
 
activationConditionRef="shibboleth.oidc.Conditions.SubjectRequired">
         <InputDataConnector ref="computedSubjectId" 
attributeNames="subjectId"/>
         <AttributeEncoder xsi:type="oidc:OIDCScopedString" name="sub" />
     </AttributeDefinition>

decommented (so all of them are active -- three in all).

According to the logs, the uid attribute is present and released.

In the logs I wasn't able to find hints whether the activation 
conditions wired on the sub definitions resolve true or not, but 
deleting them doesn't make any difference.

I wouldn't blame the attribute filter (the default taken from the 
example folder) because the client has the openid scope and actually the 
failure looks coming from the attribute resolver's phase.

I am aware i did a stupid mistake of my own. If you could suggest more 
tests I would be very very thankful,

thank you so much,

Francesco