Your organization has enabled the LDAP auth method on the path of corp-auth/.

Comprehensive and Detailed In-Depth Explanation:

When an auth method like LDAP is mounted at a non-default path (e.g., corp-auth/), the Vault UI requires specifying that path. The Vault documentation implies this via CLI examples, and UI behavior confirms it:

"If a backend was mounted using a non-default path, you need to provide it under the Mount Path option under More Options."

—Vault Tutorials: Getting Started UI (Implied)

C: Correct. Clicking “More Options” and entering corp-auth/ directs the UI to the LDAP method:

"By entering the mount path, you are directing Vault to use the LDAP auth method configured on that specific path for authentication."

—Vault Auth: LDAP

A: Dropdowns typically list methods, not paths; incorrect assumption.

B: Username doesn’t include the path in this context.

D: Namespace is unrelated to auth mount paths.