I'm running.

dovecot --version
	2.3.11.3 (502c39af9)

solr -version
	8.6.3

solr's configured to use SSL.

dovecot correctly uses SSL for transport

fts_solr = url=https://solr.example.com:8984/solr/dovecot/

adding solr-side SSL client auth,

• SOLR_SSL_NEED_CLIENT_AUTH=false

• SOLR_SSL_NEED_CLIENT_AUTH=need

I need to specify client cert for dovecot to present -- specific to the fts indexer connection.

It apparently does not use dovecot's general/global SSL configs; that^ toggle immediately breaks MUA-originated search, reporting only

2020-10-11 18:23:30 imap(myuser@example)<oKpmJW+xQKCsHgsH>: Error: fts_solr: Lookup failed: 401 Unauthorized

All other protocols SSL configs certainly work, and can be individually configured with specific key/crt pairs.

Where do I config dovecot specifically for the search backend?

I.e., where do I assign the ssl key/cert for dovecot to present as client to the solr server ?