SSH密钥无法用于Google Cloud Source仓库的问题求助

我在GitHub、GitLab及其他代码仓库均成功配置过SSH密钥，但为Google Cloud Source仓库配置时遇到权限问题。

克隆命令及错误信息 #

执行以下克隆命令：

git clone ssh://<user_name>@<domain>.com@source.developers.google.com:2022/p/<project-id>/r/omni-orchestrator

返回错误：

Cloning into 'omni-orchestrator'...
Warning: Permanently added the ECDSA host key for IP address '[<Some_IP>]:2022' to the list of known hosts.
<user_name>@<domain>.com@source.developers.google.com: Permission denied (publickey).
fatal: Could not read from remote repository.

验证访问权限 #

通过gcloud命令可正常克隆仓库，说明我拥有该仓库的访问权限：

$ gcloud source repos clone omni-orchestrator --project=<project_id>
Cloning into '/home/<user>/workspaces/<client>/gcp/omni-orchestrator'...
warning: You appear to have cloned an empty repository.
Project [<project_id>] repository [omni-orchestrator] was cloned to [/home/<user>/workspaces/<client>/gcp/omni-orchestrator].

已尝试的解决方案 #

我已按照相关官方指引创建多个不同名称的密钥，并尝试了以下两种方案，但均未解决问题，仍提示公钥权限拒绝：

1. 配置~/.ssh/config指定私钥 #

在~/.ssh目录下创建config文件，内容如下：

Host gitserv
    Hostname source.developers.google.com
    IdentityFile ~/.ssh/<user_name>_<domain>_com
    User <user_name>@<domain>.com

2. 设置GIT_SSH_COMMAND环境变量 #

执行以下命令：

<user_name>@AWESOME-<user_name>3:~/workspaces/<domain>/gcp$ export GIT_SSH_COMMAND='ssh -v -i /home/<user_name>/.ssh/<user_name>_<domain>_com -o IdentitiesOnly=yes'
<user_name>@AWESOME-<user_name>3:~/workspaces/<domain>/gcp$ git clone ssh://<user_name>@<domain>.com@source.developers.google.com:2022/p/<project_id>/r/omni-orchestrator
fatal: destination path 'omni-orchestrator' already exists and is not an empty directory.
<user_name>@AWESOME-<user_name>3:~/workspaces/<domain>/gcp$ cd ..
<user_name>@AWESOME-<user_name>3:~/workspaces/<domain>$ git clone ssh://<user_name>@<domain>.com@source.developers.google.com:2022/p/<project_id>/r/omni-orchestrator
Cloning into 'omni-orchestrator'...
OpenSSH_7.6p1 Ubuntu-4ubuntu0.7, OpenSSL 1.0.2n  7 Dec 2017
debug1: Reading configuration data /home/<user_name>/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to source.developers.google.com [74.125.133.82] port 2022.
debug1: Connection established.
debug1: identity file /home/<user_name>/.ssh/<user_name>_<domain>_com type 2
debug1: key_load_public: No such file or directory
debug1: identity file /home/<user_name>/.ssh/<user_name>_<domain>_com-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.7
debug1: Remote protocol version 2.0, remote software version Go
debug1: no match: Go
debug1: Authenticating to source.developers.google.com:2022 as '<user_name>@<domain>.com'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256@libssh.org
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:AGvEpqYNMqsRNIviwyk4J4HM0lEylomDBKOWZsBn434
debug1: Host '[source.developers.google.com]:2022' is known and matches the ECDSA host key.
debug1: Found key in /home/<user_name>/.ssh/known_hosts:7
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Offering public key: ECDSA SHA256:z7IqQohzIjyZVpxTTGKams9JxhquHb9pYhtnWMfgkuE /home/<user_name>/.ssh/<user_name>_<domain>_com
debug1: Authentications that can continue: publickey
debug1: No more authentication methods to try.
<user_name>@<domain>.com@source.developers.google.com: Permission denied (publickey).
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

内容的提问来源于stack exchange，提问作者Imad