No authentication required. Corresponds to BTA_GATT_AUTH_REQ_NONE.
Unauthenticated encryption. Corresponds to BTA_GATT_AUTH_REQ_NO_MITM.
Authenticated encryption (MITM protection). Corresponds to BTA_GATT_AUTH_REQ_MITM.
Signed data, no MITM protection. Corresponds to BTA_GATT_AUTH_REQ_SIGNED_NO_MITM.
Signed data with MITM protection. Corresponds to BTA_GATT_AUTH_REQ_SIGNED_MITM.