Mac: authentication failed due to "credential-osxkeychain is not a git command"

We've extended gitlab with gvfs protocol and encountered this error during "gvfs clone".

With debug mode of git-credential-manager on, the detailed log is as follows:

Clone parameters:
Repo URL: http://gitlab.example.com/hal/demo.git
Branch: Default
Cache Server: Default
Local Cache: /Users/Hal/.gvfsCache
Destination: /Users/Hal/gvfs/demo.git
Authenticating...—
Authenticating...
Authenticating...
Authenticating...|
Authenticating...|
Authenticating.../
Authenticating.../
Authenticating...—
Authenticating...Failed. Run 'gvfs log /Users/Hal/gvfs/demo.git' for more info.
Cannot clone because authentication failed: git: 'credential-osxkeychain' is not a git command. See 'git --help'.
Configuration::loadGitConfiguration
Configuration::ParseGitConfig
credential.helper = !/Library/Java/JavaVirtualMachines/jdk-11.0.2.jdk/Contents/Home/bin/java -Ddebug=true -Djava.net.useSystemProxies=true -jar /usr/local/Cellar/git-credential-manager/2.0.4/libexec/git-credential-manager-2.0.4.jar
diff.tool = Kaleidoscope
difftool.Kaleidoscope.cmd = ksdiff --partial-changeset --relative-path "$MERGED" -- "$LOCAL" "$REMOTE"
difftool.prompt = false
merge.tool = Kaleidoscope
mergetool.Kaleidoscope.cmd = ksdiff --merge --output "$MERGED" --base "$BASE" -- "$LOCAL" --snapshot "$REMOTE" --snapshot
mergetool.Kaleidoscope.trustexitcode = true
mergetool.keepBackup = false
mergetool.prompt = false
user.email = xxxx@xxx.com
user.name = Hal
Program::loadOperationArguments
Configuration::tryGetEntry
Configuration::tryGetEntry
Configuration::tryGetEntry
Configuration::tryGetEntry
Configuration::tryGetEntry
Configuration::tryGetEntry
Program::EnableTraceLogging
Program::get
targetUri = http://gitlab.example.com/
Program::ComponentFactory::createSecureStore
Getting a persistent token store that must be secure
Getting a persistent credential store that must be secure
Program::createAuthentication
detecting authority type
BaseVsoAuthentication::getAuthentication
BaseVsoAuthentication::detectAuthority
failed detection
authority is basic
BasicAuthentication::getCredentials
SecretStore::getTargetName
Secret::uriToName
target name = gcm4ml:git:http://gitlab.example.com
SecretStore::readCredentials
SecretCache::readCredentials
SecretCache::_getTargetName
Secret::uriToName
target name = gcm4ml:git:http://gitlab.example.com
BaseSecureStore::readCredentials
fatal: could not read Username for 'http://gitlab.example.com/': terminal prompts disabled

Start with the reported gvfs clone authentication path and reproduce the failure on macOS using the supplied GitLab URL. Inspect the configured credential.helper and the git-credential-manager debug log, then verify that authentication completes without the credential-osxkeychain error and terminal-prompt failure.