ESP_ERR_MBEDTLS_PK_PARSE_KEY_FAILED when use mqtt connect with client_key_password (IDFGH-13897)

[gl-liuqingbo]

Answers checklist.

• [X] I have read the documentation ESP-IDF Programming Guide and the issue is not addressed there.
• [X] I have updated my IDF branch (master or release) to the latest version and checked that the issue is present there.
• [X] I have searched the issue tracker for a similar issue and not found a similar issue.

General issue report

你好，我在 esp-idf/tools/test_apps/protocols/mqtt/publish_connect_test 例程下，修改ca.crt,client_pwd.crt,client_pwd.key为自签名的证书，也修改mqtt_cfg.credentials.authentication.key_password为密钥的密码，然后连接本地的mqtt服务器，但是一直得到这样的错误：

E (34252) esp-tls-mbedtls: Failed to set client pki context
E (34262) esp-tls-mbedtls: Failed to set client configurations, returned [0x8019] (ESP_ERR_MBEDTLS_PK_PARSE_KEY_FAILED)
E (34272) esp-tls: create_ssl_handle failed
E (34272) esp-tls: Failed to open new connection
E (34282) transport_base: Failed to open a new connection
E (34292) mqtt_client: Error transport connect

我的证书和密钥是没问题的，这一点我在使用另一个mqtt客户端时候验证过了。 我注意到当tls调用mbedtls_pk_parse_keyfile时，返回了MBEDTLS_ERR_PEM_UNKNOWN_ENC_ALG这样的错误，我不知道是当前esp-tls还不支持密钥密码的模式，还是说我缺少了某些配置？希望得到解答

[gl-liuqingbo]

E (23092) esp-tls-mbedtls: mbedtls_pk_parse_keyfile returned -0x1280
E (23092) esp-tls-mbedtls: Failed to set client pki context
E (23092) esp-tls-mbedtls: Failed to set client configurations, returned [0x8019] (ESP_ERR_MBEDTLS_PK_PARSE_KEY_FAILED)
E (23112) esp-tls: create_ssl_handle failed
E (23112) esp-tls: Failed to open new connection
E (23122) transport_base: Failed to open a new connection
E (23132) mqtt_client: Error transport connect