I am currently sending transactions with this code:

```
      const provider = ethers.getDefaultProvider("ropsten", {
        infura:
          "https://ropsten.infura.io/v3/ee11be9f1d1c43199618db4a7b22aa79",
      });

      const signer = new ethers.Wallet(PRIVATE_KEY);
      const account = signer.connect(provider);
      const uniswap = new ethers.Contract(
        ropstenUniswapContract,
        [
          "function swapExactETHForTokens(uint amountOutMin, address[] calldata path, address to, uint deadline) external payable returns (uint[] memory amounts)",
        ],
        account
      );
      const gasCost = ethers.BigNumber.from((+gasPrice/10) * Math.pow(10, 9));
      console.log('Computed gas cost ->', gasCost);

      const tx = await uniswap.swapExactETHForTokens(
        amountOutMin,
        path,
        to,
        deadline,
        { value, gasPrice: gasCost }
      );

      // Transaction Hash and Block
      setTransactionHash(tx.hash);
      const receipt = await tx.wait();
      console.log(receipt);

```

My question is:

How can I make MetaMask sign the transaction on my behalf instead of supplying my private key?