$re = '/\/[^\/]+\/((nifi-api\/flow)|(nifi-api))\/(?<your_field>[^\/]+)/m';
$str = '2021-04-13 23:54:59,614 INFO [NiFi Web Server-54351] o.a.n.w.s. Attempting request for (<kdave7><l.com><CN=.com, OU=Middleware Utilities,L=Phoenix, ST=Arizona, C=US>) PUT https://lpdosputb50088.phx.bvc.com:9091/nifi-api/process-groups/9c673790-e123-1a1b-9c0d-d1adf4af91cb/variable-registry
2021-04-13 23:54:59,617 INFO [NiFi Web Server-201257] o.a.n.w.s.NiFiAuthenticationFilter Attempting request for (<kdave7>><CN=lpdosputb50090.phx.aexp.com, OU=Middleware Utilities, L=Phoenix, ST=Arizona, C=US>) PUT https://lpdosputb50089.phx.abc.com:9091/nifi-api/process-groups/9c673790-e123-1a1b-9c0d-d1adf4af91cb/variable-registry
2021-04-13 23:54:41,185 INFO [NiFi Web Server-54256] o.a.n.w.s.NiFiAuthenticationFilter Attempting request for (<JWT token>) GET https://ecpnifiblaze-dev.poi.com/nifi-api/processors/cbd8ff04-0178-1000-0000-000035805b48
2021-04-13 23:54:25,867 INFO [NiFi Web Server-56517] o.a.n.w.s.NiFiAuthenticationFilter Attempting request for (<adasg17><CN=com, OU=Middleware Utilities, L=Phoenix, ST=Arizona, C=US>) GET https://lpdosputb50090.phx.p.com:9091/nifi-api/flow/process-groups/f9d9372e-b5ee-1c7b-b319-2601b4c87428';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php