Signal

URL Format

signal://[user[:password]@]host[:port]/source_phone/recipient1[,recipient2,...]

Setting up Signal API Server

Signal notifications require a Signal API server that can send messages on behalf of a registered Signal account. These implementations are built on top of signal-cli, the unofficial command-line interface for Signal (3.8k+ stars).

Popular open-source implementations include:

• signal-cli-rest-api: Dockerized REST API wrapper for signal-cli
• secured-signal-api: Security proxy for signal-cli-rest-api with authentication and access control

Common setup involves:

1. Phone Number: A dedicated phone number registered with Signal
2. API Server: A server running signal-cli with REST API capabilities
3. Account Linking: Linking the server as a secondary device to your Signal account
4. Optional Security Layer: Authentication and endpoint restrictions via a proxy

The server must be able to receive SMS verification codes during initial setup and maintain a persistent connection to Signal's servers.

Setup Resources

See the signal-cli-rest-api documentation and secured-signal-api documentation for detailed setup instructions.

URL Parameters

Host and Port

• host: The hostname or IP address of your Signal API server (default: localhost)
• port: The port number (default: 8080)

Authentication

The Signal service supports multiple authentication methods:

• user: Username for HTTP Basic Authentication (optional)
• password: Password for HTTP Basic Authentication (optional)
• token or apikey: API token for Bearer authentication (optional)

Authentication Priority

If both token and user/password are provided, the API token takes precedence and uses Bearer authentication. This is useful for secured-signal-api which prefers Bearer tokens.

Source Phone Number

The source_phone is your Signal phone number with country code (e.g., +1234567890) that is registered with the API server.

Recipients

Recipients can be:

• Phone numbers: With country code (e.g., +0987654321)
• Group IDs: In the format group.groupId

TLS Configuration

• Use signal:// for HTTPS (default, recommended)
• Use signal://...?disabletls=yes for HTTP (insecure, for local testing only)

Examples

Send to a single phone number

signal://localhost:8080/+1234567890/+0987654321

Send to multiple recipients

signal://localhost:8080/+1234567890/+0987654321/+1123456789/group.testgroup

Send to a group

signal://localhost:8080/+1234567890/group.abcdefghijklmnop=

With authentication

signal://user:password@localhost:8080/+1234567890/+0987654321

With API token (Bearer auth)

signal://localhost:8080/+1234567890/+0987654321?token=YOUR_API_TOKEN

Using HTTP instead of HTTPS

signal://localhost:8080/+1234567890/+0987654321?disabletls=yes

Optional Parameters

You can specify additional parameters in the URL query string:

• disabletls=yes: Force HTTP instead of HTTPS (same as using signals://)

Implementation Notes

The Signal service sends messages using HTTP POST requests to the API server's send endpoint with JSON payloads containing the message, source number, and recipient list. The server handles the actual Signal protocol communication.