feature: Ability to pass credentials without storing in environment file

[ArykLAnderson]

Please ignore if there is already a means to do this, but it would be nice to be able to use environment variable or bash command references for retrieving the credentials that are used to authenticate with providers and MCP servers

Ex:

  "provider": {
    "litellm": {
      "npm": "@ai-sdk/openai-compatible",
      "options": {
        "baseURL": "https://my.companies.litellm.endpoint",
        "apiKey": "$(pass litellm)"
      },
      "models": {
        "gemini-2.5-pro": {},
        "gemini-2.5-flash": {},
        "claude-4.0-sonnet": {},
        "claude-4.0-opus": {},
        "o4-mini-high": {},
        "o4-mini": {}
      }
    }
  },
"mcp": {
    "spanner-server": {
      "type": "local",
      "command": ["node", "/location/spanner-server/build/index.js"],
      "env": {
        "GOOGLE_CLOUD_PROJECT": "$GOOGLE_CLOUD_PROJECT",
        "SPANNER_INSTANCE": "$MCP_SPANNER_INSTANCE",
        "SPANNER_DATABASE": "$MCP_SPANNER_DATABASE",
        "GOOGLE_APPLICATION_CREDENTIALS": "$(pass google/spanner/mcp)"
      }
    }
}

[aspiers]

See also #231.

[rekram1-node]

[automated] Closing due to 90+ days of inactivity. Feel free to reopen if you still need this!