Function svn_auth_first_credentials 

pub unsafe extern "C" fn svn_auth_first_credentials(
    credentials: *mut *mut c_void,
    state: *mut *mut svn_auth_iterstate_t,
    cred_kind: *const c_char,
    realmstring: *const c_char,
    auth_baton: *mut svn_auth_baton_t,
    pool: *mut apr_pool_t,
) -> *mut svn_error_t

Get an initial set of credentials.

Ask @a auth_baton to set @a *credentials to a set of credentials defined by @a cred_kind and valid within @a realmstring, or NULL if no credentials are available. Otherwise, return an iteration state in @a *state, so that the caller can call svn_auth_next_credentials(), in case the first set of credentials fails to authenticate.

Use @a pool to allocate @a *state, and for temporary allocation. Note that @a *credentials will be allocated in @a auth_baton’s pool.