doc: Fix syntax error in authentication.md
doc: Fix syntax error in authentication.md

Corrected a little syntax fail now the part renders right again

Closes #11271
mvollmer/cockpit,deryni/cockpit,garrett/cockpit,mvollmer/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,deryni/cockpit,martinpitt/cockpit,cockpituous/cockpit,deryni/cockpit,martinpitt/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,garrett/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,deryni/cockpit,garrett/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,deryni/cockpit,garrett/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,garrett/cockpit,deryni/cockpit,deryni/cockpit,cockpituous/cockpit,cockpituous/cockpit,cockpituous/cockpit