[qaxi]

Fixes #153, supersedes #176, #196 and #236 (same idea, rebased on current master, single signed-off commit, with tests).

Some servers advertise mechanisms libcurl prefers but cannot complete (e.g. GSSAPI without Kerberos credentials), so login fails although PLAIN would work:

> A001 CAPABILITY
< * CAPABILITY IMAP4rev1 AUTH=PLAIN AUTH=LOGIN AUTH=NTLM AUTH=GSSAPI ...
> A002 AUTHENTICATE GSSAPI
* gss_init_sec_context() failed: No Kerberos credentials available
curl: (94) An authentication function returned an error

With curl --login-options "AUTH=PLAIN" the same login succeeds; this PR exposes that option.

An optional 7th argument is passed to CURLOPT_LOGIN_OPTIONS so the admin can pin the mechanism; existing configurations are unaffected.

Fixes #153

Supersedes #176, #196 and #236 (same idea, rebased on current master, single signed-off commit, with tests).

Changes proposed in this pull request:

• IMAP backend: new optional 7th argument loginOptions, passed to CURLOPT_LOGIN_OPTIONS (e.g. AUTH=PLAIN, AUTH=DIGEST-MD5). Unset or empty → behaviour unchanged, so existing configurations keep working.
• Admin settings UI: new optional "Login options" field for IMAP (appended as the 7th field, matching the argument position); rebuilt js/ assets.
• Unit tests for the IMAP backend (tests/unit/IMAPTest.php); curl execution moved to a small executeCurl() method so it can be stubbed, the same pattern as WebDavAuth::fetchUrl().
• README: documented the new parameter.

Tested locally: composer lint, composer cs:check, unit (46) and integration (17) tests on Nextcloud 32 / PHP 8.3, npm ci && npm run build on Node 24 (no further asset changes).

Suggested changelog line: Add optional login options (e.g. AUTH=DIGEST-MD5) for IMAP backend

Assisted-by: Claude Opus 5.5 noreply@anthropic.com
Signed-off-by: Petr Klima qaxi@seznam.cz

[qaxi]

Next attempt :-) @martinschniewind, @lazki, @damnms