Username limited to 64 characters

Steps to reproduce

1. Define on the IDP an attribute with length of >64 characters
2. Setup SSO with saml in nextcloud and use the attribute defined in 1. as UID mapping
3. try to login via SSO

Expected behaviour

Successful login

Actual behaviour

HTTP 500 internal server error, user is not logged in and in the logs are following errors:

{"reqId":"JUCv9RMwhCxuu5VqKpD7","level":3,"time":"2018-12-17T12:55:18+00:00","remoteAddr":"<......>","user":"--","app":"index","method":"POST","url":"/index.php/apps/user_saml/saml/acs","message":{"Exception":"OC\\User\\NoUserException","Message":"Backends provided no user object","Code":0,"Trace":[{"function":"getUserFolder","class":"OC\\Files\\Node\\Root","type":"->","args":["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com"]},{"file":"/opt/nextcloud/lib/private/Files/Node/LazyRoot.php","line":64,"function":"call_user_func_array","args":[[{"__class__":"OC\\Files\\Node\\Root"},"getUserFolder"],["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com"]]},{"file":"/opt/nextcloud/lib/private/Files/Node/LazyRoot.php","line":281,"function":"__call","class":"OC\\Files\\Node\\LazyRoot","type":"->","args":["getUserFolder",["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com"]]},{"file":"/opt/nextcloud/lib/private/Server.php","line":1389,"function":"getUserFolder","class":"OC\\Files\\Node\\LazyRoot","type":"->","args":["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com"]},{"file":"/opt/nextcloud/apps/user_saml/lib/UserBackend.php","line":151,"function":"getUserFolder","class":"OC\\Server","type":"->","args":["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com"]},{"file":"/opt/nextcloud/apps/user_saml/lib/Controller/SAMLController.php","line":151,"function":"createUserIfNotExists","class":"OCA\\User_SAML\\UserBackend","type":"->","args":["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com",{"urn:oid:0.9.2342.19200300.100.1.1":["user"],"urn:oid:0.9.2342.19200300.100.1.3":["user@example.com"],"urn:oid:2.5.4.4":["user"],"urn:oid:2.5.4.42":["some"],"urn:oasis:names:tc:SAML:attribute:subject-id":["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com"],"urn:oid:1.3.9999.2.3":["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com"]}]},{"file":"/opt/nextcloud/apps/user_saml/lib/Controller/SAMLController.php","line":272,"function":"autoprovisionIfPossible","class":"OCA\\User_SAML\\Controller\\SAMLController","type":"->","args":[{"urn:oid:0.9.2342.19200300.100.1.1":["user"],"urn:oid:0.9.2342.19200300.100.1.3":["user@example.com"],"urn:oid:2.5.4.4":["user"],"urn:oid:2.5.4.42":["some"],"urn:oasis:names:tc:SAML:attribute:subject-id":["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com"],"urn:oid:1.3.9999.2.3":["aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com"]}]},{"file":"/opt/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":166,"function":"assertionConsumerService","class":"OCA\\User_SAML\\Controller\\SAMLController","type":"->","args":[]},{"file":"/opt/nextcloud/lib/private/AppFramework/Http/Dispatcher.php","line":99,"function":"executeController","class":"OC\\AppFramework\\Http\\Dispatcher","type":"->","args":[{"__class__":"OCA\\User_SAML\\Controller\\SAMLController"},"assertionConsumerService"]},{"file":"/opt/nextcloud/lib/private/AppFramework/App.php","line":118,"function":"dispatch","class":"OC\\AppFramework\\Http\\Dispatcher","type":"->","args":[{"__class__":"OCA\\User_SAML\\Controller\\SAMLController"},"assertionConsumerService"]},{"file":"/opt/nextcloud/lib/private/AppFramework/Routing/RouteActionHandler.php","line":47,"function":"main","class":"OC\\AppFramework\\App","type":"::","args":["OCA\\User_SAML\\Controller\\SAMLController","assertionConsumerService",{"__class__":"OC\\AppFramework\\DependencyInjection\\DIContainer"},{"_route":"user_saml.SAML.assertionConsumerService"}]},{"function":"__invoke","class":"OC\\AppFramework\\Routing\\RouteActionHandler","type":"->","args":[{"_route":"user_saml.SAML.assertionConsumerService"}]},{"file":"/opt/nextcloud/lib/private/Route/Router.php","line":297,"function":"call_user_func","args":[{"__class__":"OC\\AppFramework\\Routing\\RouteActionHandler"},{"_route":"user_saml.SAML.assertionConsumerService"}]},{"file":"/opt/nextcloud/lib/base.php","line":987,"function":"match","class":"OC\\Route\\Router","type":"->","args":["/apps/user_saml/saml/acs"]},{"file":"/opt/nextcloud/index.php","line":42,"function":"handleRequest","class":"OC","type":"::","args":[]}],"File":"/opt/nextcloud/lib/private/Files/Node/Root.php","Line":368,"CustomMessage":"--"},"userAgent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36","version":"15.0.0.10","id":"5c179cbab3fea"}
{"reqId":"JUCv9RMwhCxuu5VqKpD7","level":3,"time":"2018-12-17T12:55:18+00:00","remoteAddr":"......","user":"--","app":"files","method":"POST","url":"/index.php/apps/user_saml/saml/acs","message":"Backends provided no user object for aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa@example.com","userAgent":"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36","version":"15.0.0.10","id":"5c179cbab413d"}

Server configuration

Operating system: Debian 9

Web server: Apache2.4

Database: MariaDB 10.1

PHP version: 7.0.33

Nextcloud version: 15.0

Where did you install Nextcloud from:
zip-file

List of activated apps:

Enabled:
  - accessibility: 1.1.0
  - activity: 2.8.2
  - cloud_federation_api: 0.1.0
  - comments: 1.5.0
  - dav: 1.8.0
  - federatedfilesharing: 1.5.0
  - federation: 1.5.0
  - files: 1.10.0
  - files_pdfviewer: 1.4.0
  - files_sharing: 1.7.0
  - files_texteditor: 2.7.0
  - files_trashbin: 1.5.0
  - files_versions: 1.8.0
  - files_videoplayer: 1.4.0
  - firstrunwizard: 2.4.0
  - gallery: 18.2.0
  - logreader: 2.0.0
  - lookup_server_connector: 1.3.0
  - nextcloud_announcements: 1.4.0
  - notifications: 2.3.0
  - oauth2: 1.3.0
  - password_policy: 1.5.0
  - provisioning_api: 1.5.0
  - serverinfo: 1.5.0
  - sharebymail: 1.5.0
  - support: 1.0.0
  - survey_client: 1.3.0
  - systemtags: 1.5.0
  - theming: 1.6.0
  - twofactor_backupcodes: 1.4.1
  - updatenotification: 1.5.0
  - user_saml: 2.1.0
  - workflowengine: 1.5.0
Disabled:
  - admin_audit
  - encryption
  - files_external
  - user_external
  - user_ldap

Nextcloud configuration:

    "system": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "something.somthing"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "15.0.0.10",
        "overwrite.cli.url": "https:\/\/something.somthing",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "maintenance": false,
        "force_language": "en",
        "updater.release.channel": "beta",
        "updater.secret": "***REMOVED SENSITIVE VALUE***",
        "loglevel": 2
    }
}

Client configuration

Browser: Chrome/Firefox

Operating system: Win10

There is also a draft for a new saml attribute urn:oasis:names:tc:SAML:attribute:subject-id (https://docs.oasis-open.org/security/saml-subject-id-attr/v1.0/saml-subject-id-attr-v1.0.pdf which explicitly allows up to 127 ASCI characters as unique identifier

Start with apps/user_saml/lib/UserBackend.php around createUserIfNotExists and apps/user_saml/lib/Controller/SAMLController.php around autoprovisionIfPossible, following the reported getUserFolder failure for a UID longer than 64 characters. Reproduce the SAML login with the supplied long subject-id value and verify that successful provisioning and login work for identifiers allowed by the referenced SAML specification.