NetworkOptions

The NetworkOptions package acts as a mediator between ways of configuring network transport mechanisms (SSL/TLS, SSH, proxies, etc.) and Julia packages that provide access to transport mechanisms. This allows the a common interface to configuring things like TLS and SSH host verification and proxies via environment variables (currently) and other configuration mechanisms (in the future), while packages that need to configure these mechanisms can simply ask NetworkOptions what to do in specific situations without worrying about how that configuration is expressed.

ca_roots() :: Union{Nothing, String}

The ca_roots() function tells the caller where, if anywhere, to find a file or directory of PEM-encoded certificate authority roots. By default, on systems like Windows and macOS where the built-in TLS engines know how to verify hosts using the system's built-in certificate verification mechanism, this function will return nothing. On classic UNIX systems (excluding macOS), root certificates are typically stored in a file in /etc: the common places for the current UNIX system will be searched and if one of these paths exists, it will be returned; if none of these typical root certificate paths exist, then the path to the set of root certificates that are bundled with Julia is returned.

The default value returned by ca_roots() may be overridden by setting the JULIA_SSL_CA_ROOTS_PATH, SSL_CERT_DIR, or SSL_CERT_FILE environment variables, in which case this function will always return the value of the first of these variables that is set (whether the path exists or not). If JULIA_SSL_CA_ROOTS_PATH is set to the empty string, then the other variables are ignored (as if unset); if the other variables are set to the empty string, they behave is if they are not set.

ca_roots_path() :: String

The ca_roots_path() function is similar to the ca_roots() function except that it always returns a path to a file or directory of PEM-encoded certificate authority roots. When called on a system like Windows or macOS, where system root certificates are not stored in the file system, it will currently return the path to the set of root certificates that are bundled with Julia. (In the future, this function may instead extract the root certificates from the system and save them to a file whose path would be returned.)

If it is possible to configure a library that uses TLS to use the system certificates that is generally preferable: i.e. it is better to use ca_roots() which returns nothing to indicate that the system certs should be used. The ca_roots_path() function should only be used when configuring libraries which require a path to a file or directory for root certificates.

The default value returned by ca_roots_path() may be overridden by setting the JULIA_SSL_CA_ROOTS_PATH, SSL_CERT_DIR, or SSL_CERT_FILE environment variables, in which case this function will always return the value of the first of these variables that is set (whether the path exists or not). If JULIA_SSL_CA_ROOTS_PATH is set to the empty string, then the other variables are ignored (as if unset); if the other variables are set to the empty string, they behave is if they are not set.

ssh_dir() :: String

The ssh_dir() function returns the location of the directory where the ssh program keeps/looks for configuration files. By default this is ~/.ssh but this can be overridden by setting the environment variable SSH_DIR.

ssh_key_name() :: String

The ssh_key_name() function returns the base name of key files that SSH should use for when establishing a connection. There is usually no reason that this function should be called directly and libraries should generally use the ssh_key_path and ssh_pub_key_path functions to get full paths. If the environment variable SSH_KEY_NAME is set then this function returns that; otherwise it returns id_rsa by default.

ssh_key_path() :: String

The ssh_key_path() function returns the path of the SSH private key file that should be used for SSH connections. If the SSH_KEY_PATH environment variable is set then it will return that value. Otherwise it defaults to returning

joinpath(ssh_dir(), ssh_key_name())

This default value in turn depends on the SSH_DIR and SSH_KEY_NAME environment variables.

ssh_pub_key_path() :: String

The ssh_pub_key_path() function returns the path of the SSH public key file that should be used for SSH connections. If the SSH_PUB_KEY_PATH environment variable is set then it will return that value. If that isn't set but SSH_KEY_PATH is set, it will return that path with the .pub suffix appended. If neither is set, it defaults to returning

joinpath(ssh_dir(), ssh_key_name() * ".pub")

This default value in turn depends on the SSH_DIR and SSH_KEY_NAME environment variables.

ssh_key_pass() :: String

The ssh_key_pass() function returns the value of the environment variable SSH_KEY_PASS if it is set or nothing if it is not set. In the future, this may be able to find a password by other means, such as secure system storage, so packages that need a password to decrypt an SSH private key should use this API instead of directly checking the environment variable so that they gain such capabilities automatically when they are added.

ssh_known_hosts_files() :: Vector{String}

The ssh_known_hosts_files() function returns a vector of paths of SSH known hosts files that should be used when establishing the identities of remote servers for SSH connections. By default this function returns

[joinpath(ssh_dir(), "known_hosts"), bundled_known_hosts]

where bundled_known_hosts is the path of a copy of a known hosts file that is bundled with this package (containing known hosts keys for github.com and gitlab.com). If the environment variable SSH_KNOWN_HOSTS_FILES is set, however, then its value is split into paths on the : character (or on ; on Windows) and this vector of paths is returned instead. If any component of this vector is empty, it is expanded to the default known hosts paths.

Packages that use ssh_known_hosts_files() should ideally look for matching entries by comparing the host name and key types, considering the first entry in any of the files which matches to be the definitive identity of the host. If the caller cannot compare the key type (e.g. because it has been hashes) then it must approximate the above algorithm by looking for all matching entries for a host in each file: if a file has any entries for a host then one of them must match; the caller should only continue to search further known hosts files if there are no entries for the host in question in an earlier file.

ssh_known_hosts_file() :: String

The ssh_known_hosts_file() function returns a single path of an SSH known hosts file that should be used when establishing the identities of remote servers for SSH connections. It returns the first path returned by ssh_known_hosts_files that actually exists. Callers who can look in more than one known hosts file should use ssh_known_hosts_files instead and look for host matches in all the files returned as described in that function's docs.

verify_host(url::AbstractString, [transport::AbstractString]) :: Bool

The verify_host function tells the caller whether the identity of a host should be verified when communicating over secure transports like TLS or SSH. The url argument may be:

1. a proper URL staring with proto://
2. an ssh-style bare host name or host name prefixed with user@
3. an scp-style host as above, followed by : and a path location

In each case the host name part is parsed out and the decision about whether to verify or not is made based solely on the host name, not anything else about the input URL. In particular, the protocol of the URL does not matter (more below).

The transport argument indicates the kind of transport that the query is about. The currently known values are SSL (alias TLS) and SSH. If the transport is omitted, the query will return true only if the host name should not be verified regardless of transport.

The host name is matched against the host patterns in the relevant environment variables depending on whether transport is supplied and what its value is:

• JULIA_NO_VERIFY_HOSTS — hosts that should not be verified for any transport
• JULIA_SSL_NO_VERIFY_HOSTS — hosts that should not be verified for SSL/TLS
• JULIA_SSH_NO_VERIFY_HOSTS — hosts that should not be verified for SSH
• JULIA_ALWAYS_VERIFY_HOSTS — hosts that should always be verified

The values of each of these variables is a comma-separated list of host name patterns with the following syntax — each pattern is split on . into parts and each part must one of:

1. A literal domain name component consisting of one or more ASCII letter, digit, hyphen or underscore (technically not part of a legal host name, but sometimes used). A literal domain name component matches only itself.
2. A **, which matches zero or more domain name components.
3. A *, which match any one domain name component.

When matching a host name against a pattern list in one of these variables, the host name is split on . into components and that sequence of words is matched against the pattern: a literal pattern matches exactly one host name component with that value; a * pattern matches exactly one host name component with any value; a ** pattern matches any number of host name components. For example:

• ** matches any host name
• **.org matches any host name in the .org top-level domain
• example.com matches only the exact host name example.com
• *.example.com matches api.example.com but not example.com or v1.api.example.com
• **.example.com matches any domain under example.com, including example.com itself, api.example.com and v1.api.example.com

Suppose you want to not verify any hosts under safe.example.com for all protocols, skip SSL host verification for just ssl.example.com, and skip SSH host verification for ssh.example.com and its immediate first level subdomains. Then you could set the following environment variable values:

export JULIA_NO_VERIFY_HOSTS="**.safe.example.com"
export JULIA_SSL_NO_VERIFY_HOSTS="ssl.example.com"
export JULIA_SSH_NO_VERIFY_HOSTS="ssh.example.com,*.ssh.example.com"

With this configuration:

• example.com would be verified for all protocols
• safe.example.com, api.safe.example.com, v1.api.safe.example.com and so on would be unverified for all transports
• ssl.example.com would be unverified for SSL/TLS transport
• sub.ssl.example.com would be verified for all transports, including SSL/TLS
• ssh.example.com and sub.ssh.example.com would be unverified for SSH only
• sub.sub.ssh.example.com would be verified for all transports

Note that the protocol of url need not match the transport mechanism being queried: the protocol of the URL is entirely discarded. The reason for this is that the typical usage of this utility function is to configure a library to enable or disable specific features like TLS host verification based on a URL. If the URL does not actually use the TLS transport mechanism, then it doesn't matter if verification for that transport is enabled or not. Moreover, different protocols can use the same transport: for example, https and ftps protocols both use TLS and ssh, scp and sftp protocols all use SSH.

A common scenario that occur behind firewalls is for all connections to external systems to go through a transparent man-in-the-middle proxy: any SSL/TLS connection to a host under example.com would be internal and should have a valid certificate but any connection outside of example.com would go through the proxy, which uses a self-signed certificate. For such a scenario the best solution would be to deploy a CA root certificate to all clients, but if that's not possible, then configuring clients to verify hosts under example.com but not verify other SSL/TLS connections would be a viable solution. In fact, as long as the man-in-the-middle proxy verifies all upstream TLS connections, this is still secure (although not private from the proxy, of course). Such a configuration can be accomplished with the following exports:

export JULIA_ALWAYS_VERIFY_HOSTS="**.example.com"
export JULIA_SSL_NO_VERIFY_HOSTS="**"

This configuration causes all domains under example.com to always be verified for all protocols, including SSL/TLS, while skipping host verification for SSL/TLS connections to all other hosts.