(core) start maintaining env vars in grist-core

Summary:
This moves and prunes a list of environment variables into core.
It is not exhaustive, or as clean as it could be. Ideally, going
forward, this will be the common place to document environment
variables.

Test Plan: documentation only

Reviewers: jarek

Reviewed By: jarek

Subscribers: jarek

Differential Revision: https://phab.getgrist.com/D3242

README.md

@@ -160,6 +160,87 @@ Grist benefits its users:
  * [Grist on AppSumo](https://appsumo.com/products/grist/) (life-time deal is sold out)
  * [Capterra](https://www.capterra.com/p/232821/Grist/#reviews), [G2](https://www.g2.com/products/grist/reviews), [TrustRadius](https://www.trustradius.com/products/grist/reviews)
 
+## Environment variables
+
+Grist can be configured in many ways. Here are the main environment variables it is sensitive to:
+
+Variable | Purpose
+-------- | -------
+ALLOWED_WEBHOOK_DOMAINS | comma-separated list of permitted domains to use in webhooks (e.g. webhook.site,zapier.com)
+APP_DOC_URL | doc worker url, set when starting an individual doc worker (other servers will find doc worker urls via redis)
+APP_HOME_URL | url prefix for home api (home and doc servers need this)
+APP_STATIC_URL | url prefix for static resources
+APP_UNTRUSTED_URL   | URL at which to serve/expect plugin content.
+GRIST_ADAPT_DOMAIN | set to "true" to support multiple base domains (careful, host header should be trustworthy)
+GRIST_APP_ROOT      | directory containing Grist sandbox and assets (specifically the sandbox and static subdirectories).
+GRIST_BACKUP_DELAY_SECS | wait this long after a doc change before making a backup
+GRIST_DATA_DIR      | directory in which to store document caches.
+GRIST_DEFAULT_EMAIL | if set, login as this user if no other credentials presented
+GRIST_DOMAIN        | in hosted Grist, Grist is served from subdomains of this domain.  Defaults to "getgrist.com".
+GRIST_EXPERIMENTAL_PLUGINS | enables experimental plugins
+GRIST_HOME_INCLUDE_STATIC | if set, home server also serves static resources
+GRIST_HOST          | hostname to use when listening on a port.
+GRIST_ID_PREFIX | for subdomains of form o-*, expect or produce o-${GRIST_ID_PREFIX}*.
+GRIST_INST_DIR      | path to Grist instance configuration files, for Grist server.
+GRIST_LOGIN_REDIRECT_HOST | host of cognito-based login helper, if applicable (usually login.getgrist.com).
+GRIST_MANAGED_WORKERS | if set, Grist can assume that if a url targeted at a doc worker returns a 404, that worker is gone
+GRIST_MAX_UPLOAD_ATTACHMENT_MB | max allowed size for attachments (0 or empty for unlimited).
+GRIST_MAX_UPLOAD_IMPORT_MB | max allowed size for imports (except .grist files) (0 or empty for unlimited).
+GRIST_ORG_IN_PATH | if true, encode org in path rather than domain
+GRIST_ROUTER_URL | optional url for an api that allows servers to be (un)registered with a load balancer
+GRIST_SERVE_SAME_ORIGIN | set to "true" to access home server and doc workers on the same protocol-host-port as the top-level page, same as for custom domains (careful, host header should be trustworthy)
+GRIST_SESSION_COOKIE | if set, overrides the name of Grist's cookie
+GRIST_SESSION_DOMAIN | if set, associates the cookie with the given domain - otherwise defaults to GRIST_DOMAIN
+GRIST_SESSION_SECRET | a key used to encode sessions
+GRIST_SINGLE_ORG | set to an org "domain" to pin client to that org
+GRIST_SUPPORT_ANON | if set to 'true', show UI for anonymous access (not shown by default)
+GRIST_THROTTLE_CPU | if set, CPU throttling is enabled
+GRIST_USER_ROOT     | an extra path to look for plugins in.
+HOME_PORT           | port number to listen on for REST API server; if set to "share", add API endpoints to regular grist port.
+PORT                | port number to listen on for Grist server
+REDIS_URL           | optional redis server for browser sessions and db query caching
+
+Sandbox related variables:
+
+Variable | Purpose
+-------- | -------
+GRIST_SANDBOX_FLAVOR | can be pynbox, unsandboxed, docker, or macSandboxExec. If set, forces Grist to use the specified kind of sandbox.
+GRIST_SANDBOX | a program or image name to run as the sandbox. See NSandbox.ts for nerdy details.
+PYTHON_VERSION | can be 2 or 3. If set, documents without an engine setting are assumed to use the specified version of python. Not all sandboxes support all versions.
+PYTHON_VERSION_ON_CREATION | can be 2 or 3. If set, newly created documents have an engine setting set to python2 or python3. Not all sandboxes support all versions.
+
+Google Drive integrations:
+
+Variable | Purpose
+-------- | -------
+GOOGLE_CLIENT_ID    | set to the Google Client Id to be used with Google API client
+GOOGLE_CLIENT_SECRET| set to the Google Client Secret to be used with Google API client
+GOOGLE_API_KEY      | set to the Google API Key to be used with Google API client (accessing public files)
+GOOGLE_DRIVE_SCOPE  | set to the scope requested for Google Drive integration (defaults to drive.file)
+
+Database variables:
+
+Variable | Purpose
+-------- | -------
+TYPEORM_DATABASE | database filename for sqlite or database name for other db types
+TYPEORM_HOST     | host for db
+TYPEORM_LOGGING  | set to 'true' to see all sql queries
+TYPEORM_PASSWORD | password to use
+TYPEORM_PORT     | port number for db if not the default for that db type
+TYPEORM_TYPE     | set to 'sqlite' or 'postgres'
+TYPEORM_USERNAME | username to connect as
+
+Testing:
+
+Variable | Purpose
+-------- | -------
+GRIST_TESTING_SOCKET | a socket used for out-of-channel communication during tests only.
+GRIST_TEST_HTTPS_OFFSET | if set, adds https ports at the specified offset.  This is useful in testing.
+GRIST_TEST_SSL_CERT | if set, contains filename of SSL certificate.
+GRIST_TEST_SSL_KEY  | if set, contains filename of SSL private key.
+GRIST_TEST_LOGIN    | allow fake unauthenticated test logins (suitable for dev environment only).
+GRIST_TEST_ROUTER | if set, then the home server will serve a mock version of router api at /test/router
+
 ## License
 
 This repository, `grist-core`, is released under the [Apache License, Version