Add parameter validation to the new generate key PKI api (#15319)

- Validate the key_type and key_bits arguments that were provided and
   perform the same default processing of 0 as we used to do for the
   generateRoot/generateIntermediate apis
 - Add a test that validates the behaviour
 - Update the field description blurbs.

builtin/logical/pki/path_manage_keys.go

@@ -19,14 +19,22 @@ func pathGenerateKey(b *backend) *framework.Path {
 				Description: "Optional name to be used for this key",
 			},
 			keyTypeParam: {
-				Type:        framework.TypeString,
-				Default:     "rsa",
-				Description: `Type of the secret key to generate`,
+				Type:    framework.TypeString,
+				Default: "rsa",
+				Description: `The type of key to use; defaults to RSA. "rsa"
+"ec" and "ed25519" are the only valid values.`,
+				AllowedValues: []interface{}{"rsa", "ec", "ed25519"},
+				DisplayAttrs: &framework.DisplayAttributes{
+					Value: "rsa",
+				},
 			},
 			keyBitsParam: {
-				Type:        framework.TypeInt,
-				Default:     2048,
-				Description: `Type of the secret key to generate`,
+				Type:    framework.TypeInt,
+				Default: 0,
+				Description: `The number of bits to use. Allowed values are
+0 (universal default); with rsa key_type: 2048 (default), 3072, or
+4096; with ec key_type: 224, 256 (default), 384, or 521; ignored with
+ed25519.`,
 			},
 			"managed_key_name": {
 				Type: framework.TypeString,
@@ -83,6 +91,11 @@ func (b *backend) pathGenerateKeyHandler(ctx context.Context, req *logical.Reque
 		keyType := data.Get(keyTypeParam).(string)
 		keyBits := data.Get(keyBitsParam).(int)
 
+		keyBits, _, err := certutil.ValidateDefaultOrValueKeyTypeSignatureLength(keyType, keyBits, 0)
+		if err != nil {
+			return logical.ErrorResponse("Validation for key_type, key_bits failed: %s", err.Error()), nil
+		}
+
 		// Internal key generation, stored in storage
 		keyBundle, err = certutil.CreateKeyBundle(keyType, keyBits, b.GetRandomReader())
 		if err != nil {

builtin/logical/pki/path_manage_keys_test.go

@@ -0,0 +1,61 @@
+package pki
+
+import (
+	"context"
+	"fmt"
+	"testing"
+
+	"github.com/hashicorp/vault/sdk/logical"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPKI_PathManageKeys_GenerateKeys(t *testing.T) {
+	b, s := createBackendWithStorage(t)
+
+	tests := []struct {
+		name           string
+		keyType        string
+		keyBits        []int
+		wantLogicalErr bool
+	}{
+		{"all-defaults", "", []int{0}, false},
+		{"rsa", "rsa", []int{0, 2048, 3072, 4096}, false},
+		{"ec", "ec", []int{0, 224, 256, 384, 521}, false},
+		{"ed25519", "ed25519", []int{0}, false},
+		{"error-rsa", "rsa", []int{-1, 343444}, true},
+		{"error-ec", "ec", []int{-1, 3434324}, true},
+		{"error-bad-type", "dskjfkdsfjdkf", []int{0}, true},
+	}
+	for _, tt := range tests {
+		for _, keyBitParam := range tt.keyBits {
+			keyName := fmt.Sprintf("%s-%d", tt.name, keyBitParam)
+			t.Run(keyName, func(t *testing.T) {
+				data := make(map[string]interface{})
+				if tt.keyType != "" {
+					data["key_type"] = tt.keyType
+				}
+				if keyBitParam != 0 {
+					data["key_bits"] = keyBitParam
+				}
+				resp, err := b.HandleRequest(context.Background(), &logical.Request{
+					Operation:  logical.UpdateOperation,
+					Path:       "keys/generate/internal",
+					Storage:    s,
+					Data:       data,
+					MountPoint: "pki/",
+				})
+				require.NoError(t, err,
+					"Failed generating key with values key_type:%s key_bits:%d key_name:%s", tt.keyType, keyBitParam, keyName)
+				require.NotNil(t, resp,
+					"Got nil response generating key with values key_type:%s key_bits:%d key_name:%s", tt.keyType, keyBitParam, keyName)
+				if tt.wantLogicalErr {
+					require.True(t, resp.IsError(), "expected logical error but the request passed:\n%#v", resp)
+				} else {
+					require.False(t, resp.IsError(),
+						"Got logical error response when not expecting one, "+
+							"generating key with values key_type:%s key_bits:%d key_name:%s\n%s", tt.keyType, keyBitParam, keyName, resp.Error())
+				}
+			})
+		}
+	}
+}